Closure methods for mines

Abstract

Treatment technology directed to using mine waste as a raw material to manufacture a mine filling product for use as a suitable precursor product or mine filling product to be used as a backfill material to close a mine. The precursor product or mine filling product retains its metals and is not be able to generate acidity. According to the disclosure, the precursor product or mine filling product, when placed in a mine, may also remove metals from mine fluids in the mine it contacts, and still retain the metals it hosted when it was a mine waste prior to it being used as a raw material to manufacture the precursor stowing backfill product.

Claims

1. A method for processing mine waste, the method comprising: receiving a mine waste including one or more heavy metals, a first heavy metal leachability, and a first sulfide concentration, wherein the mine waste, when exposed to air or water, forms acid mine drainage that includes at least some of the one or more heavy metals; and treating the mine waste to produce a product having a pH less than 7.5, wherein the product is configured to fill a mine and includes (i) a second heavy metal leachability less than the first heavy metal leachability, (ii) a second sulfide concentration less than the first sulfide concentration, and (iii) an entirety of the one or more heavy metals of the received mine waste, and wherein the product, when exposed to water or oxygen, does not form acid mine drainage.

2. The method of claim 1, wherein the mine waste has a first acidity and the product has a second acidity less than the first acidity.

3. The method of claim 1, wherein treating the mine waste comprises reducing acid-generating properties of the mine waste.

4. The method of claim 1, wherein the mine waste has a first material strength and the product has a second material strength higher than the first material strength.

5. The method of claim 1, further comprising backfilling at least a portion of the mine with the product.

6. The method of claim 1, wherein the product, when exposed to an acidic fluid, does not leach the one or more heavy metals.

7. The method of claim 1, wherein the product, when exposed to fluids that contact the product, removes heavy metals from the fluids.

8. The method of claim 1, wherein the product is a mine fill product (MFP), the method further comprising backfilling at least a portion of a mine with the MFP.

9. A method for processing mine waste, comprising: processing mine waste including heavy metals to (i) decrease a sulfide concentration of the mine waste and (ii) produce a product comprising a pH less than 7.5 and all of the heavy metals of the mine waste, wherein the product, when exposed to water or oxygen, does not form acid mine drainage; and backfilling at least a portion of a mine with the product.

10. The method of claim 9, wherein the mine waste has a first heavy metal leachability and a first sulfide concentration, and wherein the product has a second heavy metal leachability less than the first heavy metal leachability and a second sulfide concentration less than the first sulfide concentration.

11. The method of claim 9, wherein processing the mine waste comprises treating sulfides of the mine waste to form one or more stable minerals.

12. The method of claim 9, wherein processing the mine waste comprises reducing an acidity of the mine waste.

13. The method of claim 9, wherein the product is a mine fill product (MFP), and wherein, when the MFP contacts fluids including heavy metals, the MFP removes or extracts the heavy metals from the fluids.

14. The method of claim 13, wherein the fluids comprise acid mine drainage or an acidic fluid.

15. The method of claim 9, wherein the mine waste is a material that was generated by operations in the mine.

16. The method of claim 9, further comprising, prior to processing the mine waste, conditioning the mine waste by screening, crushing and/or washing the mine waste.

17. The method of claim 9, wherein the mine waste has a first material strength and the product has a second material strength higher than the first material strength.

18. The method of claim 9, wherein: the product is a mine fill product (MFP), the method further comprises applying pressure, hydraulic gradient, vibration, and/or loading sequencing to the MFP during the backfilling to increase material strength of the MFP.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a flow chart illustrating a mine waste treatment and mine closing method in accordance with embodiments of the present technology.

(2) FIG. 1A is a flow chart illustrating a mine waste treatment and mine closing method in accordance with embodiments of the present technology.

(3) FIG. 2 is a flow chart illustrating a mine waste treatment and mine closing method in accordance with embodiments of the present technology.

(4) FIG. 2A is a flow chart illustrating a mine waste treatment and mine closing method in accordance with embodiments of the present technology.

(5) FIG. 2B is a flow chart illustrating a mine waste treatment and mine closing method in accordance with embodiments of the present technology.

(6) FIG. 3 is a plot illustrating data corresponding to zinc leachability, in accordance with embodiments of the present technology.

DETAILED DESCRIPTION

(7) Described herein are various embodiments of a method of using treated mine waste to backfill and close off abandoned mines. In some embodiments, the method generally involves treating mine waste to reduce the hazardous nature of the mine waste, and subsequently using the treated mine waste to backfill and close off a mine. In some embodiments, backfilling the mine with treated mine waste minimizes or eliminates drainage of hazardous material from the mine. In some embodiments, the mine waste is treated in such a way that when the treated mine waste is used to backfill the mine, the treated mine waste interacts with hazardous material located inside the mine to thereby treat the hazardous material located in the mine.

(8) According to aspects of the present method, a treatment technology to use mine waste as a raw material to manufacture a product for use as a suitable precursor product may be used as a backfill material in a mine. The precursor product retains its metals and is not be able to generate acidity. The precursor product, when placed in a mine, may also remove metals from mine fluids in the mine it contacts, and may retain the metals it hosted when it was a mine waste prior to it being used as a raw material to manufacture the precursor stowing backfill product.

(9) Benefits of the methods described herein may include some or all of the following: treatment of mine waste to reduce or eliminate its hazardous nature; permanent storage of mine waste in a secure facility; mitigation of migration of mine drainage containing hazardous substances from a mine; and permanent closure of a mine. Based on some or all of these benefits, the methods described herein generally abate the release of hazardous substances such as heavy metals and acidity to the environment from the original mine waste and the mine.

(10) FIG. 1 is a flow chart illustrating a method 100 of treating “mine waste” 105 comprised of mine-related material 105a and/or RCRA waste 105b from a mine site to manufacture a beneficial filling product of value (i.e. a precursor mine stowing backfill product) 115, and using the filling product 115 to backfill and stow 120 to produce a filled mine void cavity 125 so that the mine or part of its workings maybe closed in accordance with embodiments of the present technology. The method 100 generally includes a step of treating and processing mine waste 105 to treat at least one hazardous component or aspect of the mine waste, for example leachable hazardous metal substances, to create a mine filling product 115 that is suitable for use as a mine backfill stowing material, and a step 120 of backfilling a mine with the treated product 115 that was manufactured 110 from mine waste resulting in a filled or closed mine 125 in part or in entirety.

(11) In step 110, one or more sources of mine waste are processed in order to treat one of more hazardous components or aspects of the mine waste 105 to generate a mine filling material 115. Mine waste 105 generally refers to material that is considered a waste product of a mining process even if exempted by the Bevill Amendment, and may include mining-related residual material 105a, but also material from a mining site that is also a waste as defined by RCRA, and pursuant to the Bevill Amendment 105b. The type and composition of the mine waste 105 subjected to the manufacturing process in step 110 is generally not limited. In some embodiments, the mine waste 105 comprises a relatively high concentration of heavy metals and/or has a relatively high acidity level. Ideally, the concentration of heavy metals, on a specific metal basis, will exceed the level at which the respective metal would leach into AMD fluid at concentrations that would exceed each respective metals' limit standards of RCRA, and the federal Clean Water and/or Safe Drinking Water Acts, as well as applicable state regulated water quality standards for the geographic location of the site. Mine waste suitable for use in step 110 is generally stored in piles, tailing ponds, embankments, or the like. The piles, tailing ponds, embankments, etc., may be located in relatively close proximity to the mine from which they were produced. As such, the mine waste processed in step 110 that manufactures a mine filling material may be sourced from a location proximate the mine into which it will be backfilled in step 120. Alternatively, the mine waste processed in step 110 can be sourced from a location remote from the mine into which it will be backfilled in step 120. Multiple sources of mine waste can be combined prior to step 110 and treated together as a common stream.

(12) The specific process used on the mine waste in step 110 is generally not limited to manufacture or produce a mine filling material product. The process used in step 110 may be any process that eliminates or minimizes any hazardous component or aspect of the mine waste. The process may also be one in which a hazardous component or aspect is chemically reacted or otherwise altered so that the hazardous substance will not leach above various water quality standards when exposed to mine fluids. In embodiments where the mine waste includes heavy metals, an objective of processing the mine waste may be to alter or otherwise impact some or all of the heavy metals. In some embodiments, the process used in step 110 is one in which heavy metal components of the mine waste are removed from the waste material or otherwise treated such that the heavy metal cannot leach out of the mine filling product when exposed to various leaching tests, including those that replicated acid rain, landfill leachate, or fluids within the mine to receive the mine filling material product. Any available technology known or that is demonstrated to be effective for this type of mine waste processing can be used. In some embodiments, the processing step 100 includes the use of any chemical treatment technology that reacts with some or all hazardous metal substances that can leach from the mine waste as a result of contact with mine fluids of the mine selected to receive the treated mine waste. Similar processes can be used to remove or treat other hazardous components of the mine waste.

(13) In addition to or in place of processing steps aimed at sequestering and/or removing hazardous components of the mine waste, the process step 110 may further include the use of processes that alter an aspect (e.g., physical property) of the mine waste. In some embodiments, the aspect of the mine waste altered by the step 110 is changing the strength of the mine waste as well as the leachable level of metals in the produced mine filling material product. Mine waste typically has a high acidity, and in some embodiments, the process step 110 includes processing the mine waste to reduce the acidity level, but also the acid generating properties of the mine waste. However, other alterations to acidity and acid-producing properties that may be beneficial in terms of reducing the hazardous nature of the mine waste may also be used so that the mine filling material remains stable and does not leach metals when placed in a mine that may or may not have mine fluids present.

(14) In some embodiments, the process step 110 is used to ensure that acid-generating properties of the mine waste cannot generate additional acidity, such as when combined with material in the mine during backfilling step 120. For example, the mine waste may be treated in such a way that it sulfides are destroyed or react to form stable mineral forms that need not be metallic or other hydroxides at an alkaline pH as a means for treating or otherwise dealing with heavy metal components of the mine waste, unless that treated material filling product is demonstrated to be stable for prolonged periods of exposure to AMD such as measured by the Modified Method 1320 where AMD is used as the extraction fluid, or if stable when tested by methods stipulated by the jurisdictional regulatory agency.

(15) With reference to FIG. 1A, processing step 110 can include one or more processing sub-steps 110a, 115. That is to say, multiple processing sub steps 110a, 115, each having their own impact on the mine waste, can be used together as part of the overall processing step 110. For example, processing step 110 may include a first processing sub-step 110a aimed at treating or removing leachable heavy metals from the mine waste, followed by a second processing sub-step 115 aimed at treating acidity and/or acid generating properties of the mine waste in the desired manner. The order of carrying out the processing sub-steps 110a, 115 is generally not limited provided that a first process sub-step 110a need not be carried out in order to successfully carry out the next processing sub step 115. Alternatively, a single step 110 may accomplish more than one objective, such as a single processing step that is capable of both treating or removing heavy metals and treating acidity and/or acid-generating properties of the mine waste and of mine waste within the mine.

(16) Acidity is the level of acid in a material. An acid-generating property of a material, as an example, is sulfide in the form of a metallic sulfide contained within ore. Sulfides will react in the presence of water, oxygen, and certain bacteria to generate acidity in the form of sulfuric acid. pH is a scale of acidity from 0 to 14, where 0 is highly acidic with low alkalinity, 7 contains and equal amount of acidity and alkalinity, and 14 is highly alkaline with low acidity. When an ore or mining related waste material that contains heavy metal sulfide substances is exposed to air, water, and bacteria, acidity is generated in the form of sulfuric acid. In that conversion, heavy metals become leachable, and the generated acid will keep them soluble as well as solubilize metals from other material the acidic fluid subsequently contacts, that in turn, will create further acidity and release metals in that material.

(17) As a result of step 110, the mine filling product is preferably converted to a treated mine waste that not only retains its own heavy metals, but also addresses acid generating properties of the mine waste. The treated mine waste produced by step 110 is also preferably treated so as to be capable of removing heavy metals from mine fluids which the treated mine material contacts during and after backfilling step 120.

(18) In some embodiments, the processing step 110 uses technology to produce a mine filling material that, in addition to treating metals and acidity to meet CERCLA and other water quality objectives, generates treated waste material in the form of dry, stackable material, paste, or slurries. The production of this type of treated mine waste product generates a material suitable for use in backfilling of caverns, chambers, voids, and open areas within a mine. In some embodiments, the processing methods used in step 110 include methods that adjust water content of the mine waste to increase or decrease the manufactured filling material product's pumpability, slump, stack-ability or other properties. This, in turn, enhances the ease of placement of the mine filling product in the mine.

(19) In some embodiments, the mine waste is processed in step 110 such that the physical strength of the product material is improved. Use of processed mined waste product having improved physical strength as leachable metal treatment capacity may be necessary for creating stops and blockages in the mine, as well as working platforms within the mine to better access voids and place the processed mine material. In still other embodiments where the mine waste treatment product is treated to improve strength and retain leachable metals, the treated mine waste can be used to prevent or otherwise minimize mine collapse that causes subsidence reflected to the ground surface where sink holes and surface grade differential settlement can cause severe damage. However, all processed mine waste will required to be processed to mitigate leachable metals if they are present to manufacture a suitable mine filling material, regardless of desires for mine filling product strength.

(20) With reference to FIG. 2, prior to, during, or after processing step 110, or between sub steps 110a, 115 of processing step 110, the method may include one or more conditioning steps 205, 210, 215 wherein the mine waste is conditioned for improved processing in step 110 to manufacture a suitable mine filling material 105 (not shown) and/or improved backfilling in step 120. An aim of the one or more conditioning steps 210 may be to condition the mine waste for improved treatment by the processing step 100. Any conditioning step that allows for improved processing in step 110 (e.g., treatment of leachable heavy metals, or their removal to below leachable levels) can be used. For example, conditioning may include screening, crushing, and/or washing the mine waste. According to aspects of the disclosure, conditioning does not include chemical treatment of the mine waste. Another aim of the one or more condition steps may be to improve the backfilling step 120. In some embodiments, the conditioning step 210 includes the removal of oversize material that would compromise or damage backfilling and/or stowing equipment that may be used in backfilling step 120.

(21) With reference to FIG. 2A, the method 100 includes a conditioning step 205 wherein oversize material is removed from the mine waste prior to processing step 110. Any method of separating oversized material from the mine waste can be used, including, e.g., classification or screening. As illustrated in FIG. 2A, the separated oversized material can be subjected to treatment step 210 to manufacture an oversize mine filling product 216 so that it may be used as a separate coarse or large graded mine filling product for direct placement in a mine, or with blending with the screened fines used to manufacture the mine filling material product 110. For example, treatment step 210 can include washing or otherwise treating the oversized material to remove any surficial contamination. Once cleaned or otherwise treated to remove contamination, the oversized material can be used for other purposes, including as part of the backfilling step 220 as described in greater detail below.

(22) With reference to FIG. 2B, condition step 205 can include crushing and/or sizing steps to reduce the size of the oversized material. Any techniques suitable for crushing and/or sizing the oversized material can be used. Once crushed, the material can be added back with the mine waste 226, either before or after step 110. Alternatively, the crushed material can be added to the mine, optional step 227, in as part of the backfilling step 220 or supplemental to step 220 (i.e., not as part of backfilling the mine, per se, but added to material already in the mine that is subsequently backfilled), or if properly processed and tested as below contaminant limits, may be used as a clean aggregate product 228 for general approved use onsite. Step 225 is filling or partially filling and closing mine void cavity. All three (3) options are illustrated in FIG. 2B. Crushed material that is contaminated or contains acid generating properties and/or heavy metals can be deposited in the mine where treated mine material is deposited or backfilled in step 220, but this may require using alternative conveyance and placement means so as not to damage or clog pumps, conveyors, and piping and other such appurtenances. As discussed previously, the treated mine material, when mixed with hazardous mine material located in the mine to be backfilled and/or material added to the mine to be backfilled (such as contaminated crushed material), can address contamination of these mine materials.

(23) While shown separately in FIGS. 2A and 2B, an embodiment of the method is also possible where both treatment steps 110 are carried out. For example, oversized material can be separated from the initial mine waste, and then subjected to a crushing step 205, followed by an optional cleaning step 210, as shown in FIG. 2B. The reverse configuration (cleaning then crushing) is also possible.

(24) While the above processing, conditioning and treatment steps have generally been described as steps being performed on the mine waste outside of the mine, it may also be possible to perform some or all of these steps inside of the mine to be backfilled. In such embodiments, only water leaves the mine workings, and such water can be treated prior to egress from the mine workings.

(25) While some of the processing techniques may require the addition of materials to the mine waste as part of altering one or more hazardous components or aspects of the mine waste, it is generally not preferred to add cement and/or pozzolanic materials to the mine waste as part of a processing step due to the fact that constituents of these materials may introduce into the mine waste heavy metals and alkalinity that generates metallic hydroxides that are not stable for prolonged periods with exposure to mine fluids, and AMD in particular. Similarly, while bacteria supplementation of the mine waste is also possible, it is generally not preferred, as the organisms may be taxis to external stimuli, such as food source and oxygen levels, and therefore difficult to control and facilitate their desired in-mine living conditions suitable to sustainable propagation of the selected species and strains.

(26) In summary, processing step 110 generally aims to manufacture, physically process, condition, and/or chemically treat mine waste to yield a processed mine filling product having beneficial re-use characteristics related to heavy metal and other constituent leachability of the mine waste and the mine AMD to meet criteria herein described.

(27) In step 120, the processed mine waste is an embodied mine filling product used to backfill and, in some embodiments, close off a mine, or partial workings therein. The specific techniques and equipment used for the backfilling step 120 are generally not limited provided the techniques and equipment adopt the use of the mine waste processed in step 110. Those skilled in the art of material stowing in a mine will also be aware of methods, system, and approaches to control the fill with respect to stacking, diversion, dams, bulkheads and other such means to position and retain the processed mine waste during the filling operational sequences. Backfilling step 120 may be carried out using means and methods including: hydraulic or pneumatic stowing; dry material backfilling, mechanized (conveyor, ore car, conveyors, haulers, muck loaders and trucks, muck buckets, and other such means) backfilling, pneumatic backfilling, paste and paste cemented backfilling, self-slide backfilling (for shafts, and steep-inclined seams and stopes), and other of the like; injection pumping of grout, paste, foam in-fill, fluid or slurries through pipes installed within the mine shafts, tunnels, adits, and drifts, and/or via drilled bore holes penetrating from surface to a mine goaf or goaves, bulkheads, dams, barricades, etc. installations for material retention and diversion within the mine workings; and dewatering, drainage, packing, and densification of beneficial re-use material.

(28) The mine to be backfilled in step 120, such as mine caverns and mine voids, may be accessed by existing shafts or boreholes into the void space or spaces from above their location. As with typical filling operations, many options exist for ensuring the voids of mines are properly filled and controlled during the backfilling step 120. Safe access and egress to the mine should be maintained during backfill step 120. Efforts can also be made to ensure access is maintained to far reaches of the mine so that such area can be backfilled.

(29) Mine suitable for use in the method 100 described herein are generally not limited. In some embodiments, the mine to be backfilled in step 120 has a minimal volume of mine fluids, with static or only minimal flow. Mine fluid is also preferably of an acidic pH, although the methods described herein can also be used on mines having mine fluid of any pH. Deeper mine pools (i.e., mines having larger mine fluid volumes) may also be used to receive the processed mine waste in backfill step 120 provided mine water displaced by the deposition of processed mine waste is removed and treated for reuse or discharged as approved by appropriate regulatory agencies.

(30) In some embodiments, the backfilling step 120 results in the mines being completely or partially sealed permanently with the processed mine waste, including filling all mine voids with the processed mine waste to prevent intrusion of water.

(31) Because of a mine's typical subterranean location, the final closure may be protected from some or all factors that would otherwise create risk of failure to above ground repositories. For example, mine cavities and caverns are typically surrounded by rock and hard mineral materials. With properly processed mine waste that yields a suitable mine filling material for backfill stowing placement and installation in the mine, the filled mine will be well protected from any number of forces. Additionally, when properly backfilled via step 120, void spaces will be filled with processed mine waste so that water pressure from a formation surrounding the former void is equalized and water will not drain into and displace the stowed processed mine waste. As such, migratory water within the entire formation outside of mined voids will find other alternative conveyance avenues such as formation cracks, seams, fissures, and other pathways, thus avoiding the processed mine waste as a result of reduced hydraulic pressure and resistance than that of the filled void.

(32) The mine filling product may contain mine waste particulates and fines that when placed in the mine may migrate from the filling product after placement and fill and seal fissures, pores, micro-fractures or other small conveyance, thus impeding migratory water egress and ingress to the mine. As such, in some embodiments, step 120 is carried out such that material fines within the treated mine waste will migrate into and seal the various conveyance pathways if/when carried by water, including those naturally existing or those created during mineral disruption and extraction emanating from the extraction workings hard rock or mineral surfaces. As such, a mine properly filled with the processed mine waste is a sealed system that prevents ingress and egress of mine fluids.

(33) In some embodiments, the methods described herein may include the capture, collection, and draw-down of mine fluids and drainage prior to and/or during backfill step 120. Collected water may be used to process the mine waste in step 110, and/or be used as a carrier to facilitate processed mine waste placement in step 120. Alternatively, the water may be treated for discharge or another reuse.

(34) As described previously, oversized material separated from the mine waste can be used in the backfill step 120. In general, this oversize material is best used where structural enhancement is needed to secure mine ports of access, vent shafts, tunnels, and other ingress/egress openings, and/or construct roads, work pads and for armoring and securing unstable surfaces. The density, hardness, and size cause oversize material to be a valuable resource suitable for use in aiding the placement of processed mine waste, and to secure the mine. The oversize material can also serve as a clean backfill or construction aggregate product. It may be blended with other additives such as asphalt or cement and placed to armor or permanently seal and secure portals, shafts, adits and the like before or after the processed mine waste is placed in the mine via step 120.

(35) In some embodiments, the processed mine waste can be used to create an effective chemical barrier or layer within the mine to hold untreated mine wastes and prevent their exposure to mine fluids and the factors that cause the formation of AMD. When used in this manner, not all mine waste will require processing, as the installed layer will provide the protection and isolation needed to prevent contact with mine fluids and the formation of AMD.

EXAMPLES

(36) In the 1980's RCRA regulations were promulgated that defined the differences between hazardous and non-hazardous wastes. The regulations also stipulated that each of these waste types required different means of management and disposal. Solids wastes that were classified as hazardous required more stringent management and disposal efforts, and those that were non-hazardous. Landfills for non-hazardous wastes were less costly to design, construct, and manage, while hazardous waste landfill were much more costly, harder to permit, required more operation and management efforts that included the requirement to treat the hazardous waste at the landfill prior to its internment. As such, there was, and still is, a significant disposal cost differential between hazardous and non-hazardous waste. Further, the costs for transportation of hazardous wastes from their point of origin to the landfill disposal facility are significantly more than those for non-hazardous waste. As a result of these cost differentials, there was an economic need for the development treatment technologies for generators of hazardous waste to process the material at its point of origination to render the waste non-hazardous to allow for its less costly landfill management.

(37) Many technology developers looked at the chemistry of various wastes types and chemicals that caused waste to be hazardous. For solid waste such as soil that contained heavy metals that leached in excess of the RCRA toxicity criteria, treatment technologies largely relied on passing the TCLP extraction test where metals in waste were retained by the waste when extracted by a synthetic landfill leachate fluid as described elsewhere, herein. Many technologies utilized cements, fly ash, kiln dusts and others that generated strength to prevent metals from leaching, but also the formation of highly buffered treated waste that maintained an alkaline pH, thus metallic hydroxides, that were able to withstand the TCLP single extraction test's chemistry. These technologies were and are still prevalent, however, due to the amount of reagent required to meet the RCRA toxicity leachability limits, treated end-products were significantly more voluminous and had extensive mass increases for the untreated waste because of the reagent mass added, but also from water required to hydrate and/or cause the formation of the metallic hydroxides. There remained a need for other forms of treatment that did not cause these increases in mass and volume, and thus high cost related to material handling, transportation, and the final mass interned at the landfill.

(38) This need was resolved by the development of other technologies that did not rely on strength or the formation of metallic hydroxides, or at least, the need to maintain a high buffering capacity at an alkaline pH. Most of these non-hydroxide or strength related technologies focused on the use of specialty reagents that formed metal compounds in the waste that have low solubility products. Many technologies were developed that utilized singular or multiple reagents containing silicates, carbonates, sulfides, phosphates, or other such constituents that form insoluble metal species with very low solubility products, and where the metal leachability remains very low, even in the low pH of the TCLP extraction method. As also stipulated by RCRA, only eight (8) metals are required to be evaluated for their toxicity levels in TCLP extract. Many of these technologies have been well proven over many years in the commercial arena with some specializing on one or two metals, and some are able to treat all of the RCRA metals. It is noted that most technologies have not been applied to non-RCRA that are typically found at mine sites or in mine wastes, such as aluminum, cobalt, copper, manganese, nickel, and zinc to name a few.

(39) The examples presented herein present treatment data from three (3) technologies that do not rely on physical strength or the formation of metallic hydroxides to treat heavy metal leachability. As required in the present disclosed method, treated precursor product must be able to retain heavy metals over a prolonged period of exposure to acidity, as well as remove metals from the acidic fluid found within mines or mine sites. The three (3) technologies presented in the examples utilize phosphates, sulfides, sulfates, carbonates, or the like, and all generate an end-product with heavy metal precipitates or minerals that resist leaching in acidic conditions as they do not form metallic hydroxides.

(40) The data in Tables 1, 2, and 3 present treatment results of various materials that contained leachable heavy metals at NPL Superfund Sites. Different commercially available treatment technologies for leachable heavy metals in soils or sediments were identified as having potential for use in the present innovation despite their intended use of rendering RCRA Subtitle C hazardous waste to a non-hazardous RCRA solid waste under the RCRA toxicity rule. Data as reported was all generated in accordance with USEPA SW-846 Test Methods for the Evaluating Solids Waste and with the intent of disposing material at a remediation project site in an engineered repository constructed. No other “off-the-shelf” commercially available technologies were considered for inclusion as examples, except the EPA lime solids based on the conventional use of lime and hydroxides. Other non-hydroxide forming technologies are available for implementation in the present method and their non-use in the examples does not preclude them in any manner, provided that any selected technology can treat RCRA metals present in mine waste to meet the toxicity limit for hazardous waste, but also treat the broad-spectrum hazardous metal substances found in mine wastes and AMD to respective metal leachable levels that are below various state and federal water quality standards applicable to the specific mine site.

(41) Other technologies were identified that combined other forms of reagents with cement or hydroxides, but they neither purported to treat all heavy metals found at mine sites, nor did they show the ability to withstand the robust agitation and prolonged acidity exposure to the USEPA's Method 1320 (Multiple Extraction Procedure) for acid rain or other improperly constructed and maintained landfills. The technologies considered herein are examples for possible candidates for the manufacturing of the required mine filling product of the present method for use as an in-mine stowing backfill, did at least, not rely on metallic hydroxide formation to achieve heavy metal stability at an elevated alkaline pH that had to be maintained for long-term stability in a mine characterized by fluid presence, acidity, and/or multiple migratory hazardous metal substances. As technologies are identified, envisioned, developed, and made available for the treatment of leachable heavy metals found in mine wastes and in mines, they could be suitable candidates for inclusion. Importantly, the technology identified and presented in Table 3 and FIG. 3 does meet the minimum criteria of the present invention based on the testing data presented in the example.

(42) It is noted that treatment technology data is presented to show the requirements needed under the present innovation for manufacture of a mine filling material product for the backfill stowing within a mine that contains mine fluids, a broad-spectrum of heavy metals, and acidity. It is important to also note that each of the technologies met one criteria for the parameters analyzed, that being the general requirement of reducing metal leachability without relying upon metallic hydroxide formation. However, the long-term stability of treated materials of Tables 1 and 2 were only evaluated using Method 1320 using the EPTox and SPLP-acid rain extraction fluids, and not acid mine fluids as that testing had not been published or made known in prior art. Regardless, each of these respective technologies generated data as examples of possible candidates for use in this disclosed method to process raw material mine waste and manufacture a suitable precursor mine backfill stowing material, but further testing would be required for at least minimal acceptance confirmation as other metals require evaluation as well as their exposure to AMD or similar acidic fluids.

(43) While treated material in Table 1 and Table 2 clearly demonstrated stability of lead to acid rain exposure derived from the respective treatment technologies, Table 2 also presents other metals of concern for the material treated based on target parameters generally associated with the BPMD NPL site, but also to only acid rain. Another third technology was evaluated that also showed promise in rendering the multitude mine waste metals non-leachable in the standard Method 1320 for acid rain. Based on reagent availability, that treated mine waste was then evaluated under the modified Method 1320 using AMD as the extraction fluid. Again, selection of this treatment technology for consideration in this present innovation was only a convenience, and not intended to eliminate the other exampled technologies, or those that are also available for evaluation and use.

(44) Table 3 presents the data where lime-solids from the USEPA's Gold King Mine AMD water treatment system in Gladstone, Colo. (BPMD NPL Site) were processed and using AMD from the American Tunnel located in close proximity to the AMD lime treatment system. The American Tunnel (AT) is a bulk headed mine that has a restricted flow of AMD egressing the mine on a continuous basis. The table includes characterization data for the AT AMD used as the extraction fluid, total metals in the GKM lime solids that were treated, and the treated and untreated waste extraction heavy metal data of the various metals in each of the ten (10 sequential extractions of USEPA's Method 1320 (MEP) as modified using AMD as the extraction fluid), noting that both treated GKM lime solids and untreated lime-solids were subjected to the modified Method 1320.

(45) To visually illustrate the performance of the manufactured precursor product suitable for use as an in-mine stowing backfill at an abandoned, FIG. 3 graphically presents the data for zinc from Table 3. Similar leachability curves can be plotted for each parameter in Table 3 if they are respectively graphed as metal concentration vs. MEP extraction number for the AMD, the untreated lime solids, and the treated lime solids.

(46) TABLE-US-00001 TABLE 1 Total and Leachable Lead for On-Site Waste Management Item Total Pb (mg/Kg) TCLP Pb (mg/L) MEP (mg/L) Untreated 37,600 90.1 Treated 27,300 0.331 MEP-1 <0.132 MEP-2 <0.132 MEP-3 <0.132 MEP-4 <0.132 MEP-5 <0.132 MEP-6 <0.132 MEP-7 <0.132 MEP-8 <0.132 MEP-9 <0.132 MEP-10 <0.132 NOTES: 1) MEP-1 was performed using USEPA Method 1310 (EPTox) 2) MEP 2-10 were performed using USEPA Method 1312 (Synthetic Precipitation Leaching Procedure - Acid Rain)

(47) The example presented in Table 1 includes data for lead, which was the only parameter of concern for the waste material at this site. As an untreated material that was a waste as defined by RCRA, the material was deemed a hazardous waste due to its toxicity for lead being in excess of 5 mg/L, the RCRA toxicity limit. No other RCRA metals were present in excess of their toxicity limit for its hazardous waste classification. After treatment, the material was non-hazardous as shown by its TCLP (EPA Method 1311) lead level. Based on Method 1320 using the method's synthetic acid rain (Method 1312) as an extraction fluid, test results on the treated material would allow the material to be managed in an onsite repository. As an example of treated material for use in the present method as a produce a suitable mine filling material product for backfill stowing within a mine, additional testing would have needed to be completed to assure lead and other RCRA and non-RCRA metals would have needed to have been evaluated, however with such a reduction of leachable lead as noted, the technology used to process this material is a likely candidate for use in the present method. It did not rely on metallic hydroxides to form insoluble metal substances at elevated pH.

(48) TABLE-US-00002 TABLE 2 Heavy Metal Treatment Data Bonita Peak Mining District NPL Site Cement Creek Sediments, Gladstone, CO: Treated Sediments - US EPA Method 1320 (Multiple Extraction Procedure) Data 1 EP-1310 2 3 4 5 6 7 8 9 10 Metal Total (mg/Kg) (mg/L) SPLP-1312 (mg/L) Aluminum 9,130 0.279 0.216 0.461 0.164 0.062 0.174 0.406 0.556 0.562 1.65 Arsenic 44 <0.100 <0.100 <0.100 <0.100 <0.100 <0.100 <0.100 <0.100 <0.100 <0.100 Cadmium 8 <0.050 <0.050 <0.050 <0.050 <0.050 <0.050 <0.050 <0.050 <0.050 <0.050 Copper 274 0.026 <0.050 <0.020 0.021 0.025 <0.080 0.045 0.102 0.130 0.182 Iron 72,300 1.86 0.564 0.771 0.397 0.337 0.505 1.40 1.48 1.51 3.58 Lead 1,040 <0.100 <0.100 <0.100 <0.100 <0.100 <0.100 <0.100 <0.100 <0.100 <0.100 Manganese 738 4.28 0.788 0.550 0.406 0.828 0.596 0.661 0.584 0.397 0.393 Zinc 897 0.189 <0.050 <0.050 <0.050 0.128 0.151 0.244 0.291 0.230 0.235

(49) Table 2 presents the data for metals of concern in sediments obtained from Cement Creek in Gladstone, Colo. downstream from the AMD discharge from Gold King Mine in the BPMD NPL site and prior to the installation and operation of EPA's GKM AMD lime-polymer treatment system. While metals in the sediments prior to treatment were below RCRA levels for hazardous waste toxicity, the concentrations of the metals as totals (mass of metal per mass of sample) in the sediments were elevated. As in Table 1, treated material was subjected to USEPA Method 1320 using the specified extraction fluid (synthetic acid rain for the western US). Each of the metals responded favorably to treatment with the end product having very limited concentrations of leachable metals in the acid rain extraction fluid. As such, this technology is also a candidate for use in the present method, however, treated material should also be subjected to the modified Method 1320 extraction procedure where AMD is used as the extraction fluid to further confirm the technology's use to manufacture the desired precursor mine backfill stowing material to ensure it will retain its stability and remove acidity and heavy metals from the fluids within the mine. It did not rely on metallic hydroxides to form insoluble metal substances at elevated pH.

(50) TABLE-US-00003 TABLE 3 Solids Treatment Technology Field Study Data Gold King Mine (GKM) Acid Mine Drainage (AMD), Gladstone, Colorado Bonita Peak Mining District (BPMD) NPL Site Method 1320 - Modified (American Tunnel AMD Water used as Extraction Fluid) pH Al As Cd Co Cu Baseline American Tunnel AMD (mg/L - Totals) 3.02 4.61 <0.0050 <0.0050 0.148 0.0201 Untreated GKM EPA Lime Solids (mg/Kg - Totals)>> 8.29 60,100 70.5 175 146 13,100 Extraction 1 American Tunnel AMD (mg/L - Totals) 3.02 4.61 <0.0050 <0.0050 0.148 0.0201 Untreated GKM EPA Lime Solids (mg/L) <0.250 0.010 0.257 0.0585 0.0464 MBTTreated GKM Lime Solids (mg/L) <0.250 <0.010 0.005 0.0034 0.0181 Extraction 2 American Tunnel AMD (mg/L - Totals)>> 3.02 4.61 <0.0050 <0.0050 0.148 0.0201 Untreated GKM EPA Lime Solids (mg/L in extract)>> <0.250 0.011 0.703 0.264 0.0473 MBT Treated Lime Solids (mg/L) <0.250 <0.010 0.006 0.0052 0.0271 Extraction 3 American Tunnel AMD (mg/L - Totals)>> 3.02 4.61 <0.0050 <0.0050 0.148 0.0201 Untreated GKM EPA Lime Solids (mg/L in extract)>> <0.250 <0.010 1.30 0.430 0.0587 MBT Treated Lime Solids (mg/L) <0.250 <0.010 0.007 0.0080 0.0154 Extraction 4 American Tunnel AMD (mg/L - Totals)>> 3.02 4.61 <0.0050 <0.0050 0.148 0.0201 Untreated GKM EPA Lime Solids (mg/L in extract)>> <0.250 <0.010 1.75 0.452 0.0746 MBT Treated Lime Solids (mg/L) <0.250 <0.010 0.009 0.0099 0.0255 Extraction 5 American Tunnel AMD (mg/L - Totals)>> 3.02 4.61 <0.0050 <0.0050 0.148 0.0201 Untreated GKM EPA Lime Solids (mg/L in extract)>> 0.283 0.016 1.77 0.351 0.540 MBT Treated Lime Solids (mg/L) <0.250 <0.010 0.006 0.0148 0.0200 Extraction 6 American Tunnel AMD (mg/L - Totals)>> 3.02 4.61 <0.0050 <0.0050 0.148 0.0201 Untreated GKM EPA Lime Solids (mg/L in extract)>> 1.45 0.016 1.70 0.261 1.7300 MBT Treated Lime Solids (mg/L) <0.250 <0.010 0.007 0.0179 0.0206 Extraction 7 American Tunnel AMD (mg/L - Totals)>> 3.02 4.61 <0.0050 <0.0050 0.148 0.0201 Untreated GKM EPA Lime Solids (mg/L in extract)>> 7.31 0.017 1.27 0.214 3.8200 MBT Treated Lime Solids (mg/L) <0.250 <0.010 0.012 0.0227 0.0067 Extraction 8 American Tunnel AMD (mg/L - Totals)>> 3.02 4.61 <0.0050 <0.0050 0.148 0.0201 Untreated GKM EPA Lime Solids (mg/L in extract)>> 11.40 <0.050 1.17 0.248 8.4200 MBT Treated Lime Solids (mg/L) <0.250 <0.010 0.012 0.0297 0.0120 Extraction 9 American Tunnel AMD (mg/L - Totals)>> 3.02 4.61 <0.0050 <0.0050 0.148 0.0201 Untreated GKM EPA Lime Solids (mg/L in extract)>> 17.0 <0.050 0.51 0.174 8.85 MBT Treated Lime Solids (mg/L) <0.250 <0.010 0.016 0.0417 0.0168 Extraction 10 American Tunnel AMD (mg/L - Totals)>> 3.02 4.61 <0.0050 <0.0050 0.148 0.0201 Untreated GKM EPA Lime Solids (mg/L in extract)>> 18.50 <0.050 0.400 0.196 10.3 MBT Treated Lime Solids (mg/L) <0.250 <0.010 0.011 0.0393 0.0118 Fe Pb Mn Ni Zn Baseline American Tunnel AMD (mg/L - Totals) 101 0.0196 44.9 0.0862 18.5 Untreated GKM EPA Lime Solids (mg/Kg - Totals)>> 246,000 64.1 22,600 103 39,200 Extraction 1 American Tunnel AMD (mg/L - Totals) 101 0.0196 44.9 0.0862 18.5 Untreated GKM EPA Lime Solids (mg/L) 0.653 <0.005 64.3 0.0471 0.936 MBT Treated GKM Lime Solids (mg/L) <0.250 0.006 1.29 0.0231 <0.100 Extraction 2 American Tunnel AMD (mg/L - Totals)>> 101 0.0196 44.9 0.0862 18.5 Untreated GKM EPA Lime Solids (mg/L in extract)>> 0.790 <0.005 81.8 0.0988 12.0 MBT Treated Lime Solids (mg/L) 0.356 0.011 2.39 0.0276 0.107 Extraction 3 American Tunnel AMD (mg/L - Totals)>> 101 0.0196 44.9 0.0862 18.5 Untreated GKM EPA Lime Solids (mg/L in extract)>> 0.766 <0.005 75.7 0.173 37.0 MBT Treated Lime Solids (mg/L) <0.250 0.007 4.10 0.0342 <0.100 Extraction 4 American Tunnel AMD (mg/L - Totals)>> 101 0.0196 44.9 0.0862 18.5 Untreated GKM EPA Lime Solids (mg/L in extract)>> <0.250 <0.005 65.4 0.231 61.1 MBT Treated Lime Solids (mg/L) 0.434 0.007 5.47 0.0312 0.131 Extraction 5 American Tunnel AMD (mg/L - Totals)>> 101 0.0196 44.9 0.0862 18.5 Untreated GKM EPA Lime Solids (mg/L in extract)>> 0.617 0.006 57.2 0.203 72.2 MBT Treated Lime Solids (mg/L) 0.390 0.009 8.59 0.0523 <0.100 Extraction 6 American Tunnel AMD (mg/L - Totals)>> 101 0.0196 44.9 0.0862 18.5 Untreated GKM EPA Lime Solids (mg/L in extract)>> 0.353 <0.005 52.8 0.170 67.3 MBT Treated Lime Solids (mg/L) 0.461 0.012 10.80 0.0435 0.106 Extraction 7 American Tunnel AMD (mg/L - Totals)>> 101 0.0196 44.9 0.0862 18.5 Untreated GKM EPA Lime Solids (mg/L in extract)>> 0.324 <0.005 47.9 0.146 42.8 MBT Treated Lime Solids (mg/L) <0.250 <0.005 13.3 0.0443 <0.100 Extraction 8 American Tunnel AMD (mg/L - Totals)>> 101 0.0196 44.9 0.0862 18.5 Untreated GKM EPA Lime Solids (mg/L in extract)>> <0.250 <0.005 61.4 0.167 34.6 MBT Treated Lime Solids (mg/L) 0.274 <0.005 17.4 0.0569 <0.100 Extraction 9 American Tunnel AMD (mg/L - Totals)>> 101 0.0196 44.9 0.0862 18.5 Untreated GKM EPA Lime Solids (mg/L in extract)>> <0.250 <0.005 47.4 0.113 29.4 MBT Treated Lime Solids (mg/L) 0.444 0.006 24.1 0.0584 0.111 Extraction 10 American Tunnel AMD (mg/L - Totals)>> 101 0.0196 44.9 0.0862 18.5 Untreated GKM EPA Lime Solids (mg/L in extract)>> 0.831 0.007 53.1 0.143 23.7 MBT Treated Lime Solids (mg/L) 0.288 <0.005 22.60 0.5270 <0.100

(51) Table 3 presents the data for untreated AMD fluid from the AT, the untreated EPA GKM Lime solids, and the treated EPA GKM lime solids. The data shows that the pH of the AMD is 3.02, which is at least as or more acidic than the pH conventional to TCLP, SPLP, and MEP lab-grade reagent prepared extraction fluids of their respective EPA test methods (1311, 1312, and 1320), but the AMD contained high levels of hazardous heavy metal substances that the EPA method fluids did not. The data also shows the concentration of those heavy metals in the AMD as sourced from the mine. The data also shows that both the untreated EPA lime solids and the mine waste generated from the treatment of the Gold King Mine AMD contain elevated levels of total and metals. However, and in view of the MEP extraction results using AT AMD as the extraction fluid in ten (10) sequential extractions, only the treated GKM lime solids retained its metals in the acidity of the AMD fluid and also removed metals from the AMD in each extraction. As a reminder, the same solid sample aliquot of the material being tested was moved through each of ten extractions, but with fresh extraction (AMD) fluid used at each step and with each metal respectively quantified in each extract.

(52) This data shows that the technology used to evaluate a possible manufactured mine filling material product in Table 3 is well suited for use in this present method. This mine filling product will not only retain its heavy metals when backfilled or stowed in a mine with AMD being present, it will also address acidity, and remove heavy metals from the AMD itself. As with the other technologies, it does not rely on the formation of metallic hydroxides to reduce the leachability of heavy metals.

(53) FIG. 3 presents the data for only zinc from Table 3 as an example of only one leachable metal often found in mine waste and mines. It is clear that the treated material retains zinc through all ten (1) extractions and removes the metals from the AT AMD. Further, lime solids from the EPA GKM water treatment system failed to withstand the rigors of the modified Method 1320 throughout the entire test where AMD was used in each of the extractions as the eluant fluid.

(54) As such, untreated lime-solids are not adequate for use as a precursor in-mine backfill stowing material. Zinc was released when the acidity of the AMD from the mine overcame the pH buffering capacity of material, and the lime solids failed to remove heavy metals from the AMD after only the 2.sup.nd extraction. In all likelihood, a vast majority of the total 39,200 mg/Kg zinc in the untreated lime solids sample was leached from the waste by the 6.sup.th or 7.sup.th extraction. Looking at Table 3, other leachable metals that also caused untreated lime-solids to be unsuitable for precursor product backfill use included: aluminum, cadmium, cobalt, copper, manganese, and nickel.

(55) As discussed, the RCRA defines whether a material is a waste or not, and if a waste, whether or not the waste is hazardous or non-hazardous. The Bevill Amendment exempts much various mine related materials from RCRA regulation, such that this exempted material is not a waste under RCRA. However, mine related materials still contain hazardous substances that can leach and contaminate and pollute water and waterways. Regardless, and despite the Bevill Amendment, the exempted mine waste material still is a source of contamination and pollution. The present invention utilizes mine related materials and mine waste (whether a RCRA waste or not) as a raw material to manufacture or beneficiate the mine related material or mine waste into a new product of economic value. The new product or precursor product is then used as a legacy mine stowing backfill material. This distinguishing characteristic of the disclosed method is in concert with RCRA and Bevill regulations where both solid waste and mine related materials are beneficiated and used to create a new resource of value, both economic and with respect to pollution mitigation of mine waste AND legacy/abandoned and operating mines.

(56) In consideration of mine waste treatment to manufacture a suitable precursor product for use in the present innovation, the resultant leachability data of that product at minimum must pass the RCRA toxicity limit if the material is a RCRA hazardous waste. As such, it must also pass the EPA's Land Disposal Restriction upon treatment. For mine waste that is exempt from the solid waste regulations of RCRA under the Bevill Amendment, the mine waste must still not release hazardous substances as defined by CERCLA into waters and waterways where constituent concentrations may need to meet the USEPA Clean Water and Safe Drinking Water Act limits, but also those limits that may be imposed by the respective state where the mine waste and mine is located. The treatment technology to be selected for precursor product manufacture may need optimization to achieve these or other site-specific limits if required by the various jurisdictional regulatory agencies.

(57) As long as prevailing weather continues to cause precipitation and its melt or immediate run-off and percolation into mines, AMD will be a continued source of contamination that will require prolonged and costly treatment, or AMD will carry hazardous substance constituents to downgradient waterways and supplies unless a means exists to prevent water intrusion into the mine.

(58) By using a treatment technology that performs as shown, a precursor in-mine stowing backfill product can be manufactured for its use as part of the present method to ultimately fill and close a mine such that the mine waste and the mine are prevented from releasing hazardous heavy metal substances and acidity separately identified in both the mine waste(s) and mines with this present method. Thus, the hazards and pollutants emanating from historic mining district sites where offending mine waste and mines are located can both be safely and permanently resolved with a single beneficial solution to better human health and the environment.

(59) From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the scope of the invention. Accordingly, the invention is not limited except as by the appended claims.