PROCESS OF PREPARING A CEMENTED PASTE BACKFILL MATERIAL

Abstract

A process of preparing a cemented paste backfill material, the material including ground mine tailings, a hydraulic binder and water, wherein the solids content of the backfill material is 70-82 wt.-%, the process including a) providing a dry premix, the premix including the hydraulic binder, a superplasticizer and optionally a defoaming agent, b) mixing the dry premix with the ground mine tailings and water.

Claims

1. A process of preparing a cemented paste backfill material, said material comprising ground mine tailings, a hydraulic binder and water, wherein solids content of the backfill material is 70-82 wt-%, the process comprising: a) providing a dry premix, said premix comprising the hydraulic binder, a superplasticizer and optionally a defoaming agent, b) mixing said dry premix with the ground mine tailings and water.

2. The process according to claim 1, wherein the premix is provided in powder form.

3. The process according to claim 1, wherein the hydraulic binder comprises Portland cement.

4. The process according to claim 1, wherein the hydraulic binder comprises ground granulated blast furnace cement at a content comprised between 70 and 90 wt.-% of the total hydraulic binder, or fly ash between 40 and 70 wt.-% of the total hydraulic binder

5. The process according to claim 1, wherein the amount of dry premix is selected so that the backfill material has a content of hydraulic binder of 2-14 wt.-%.

6. The process according to claim 1, wherein the dry premix additionally comprises a stabilising agent.

7. The process according to claim 1, wherein the superplasticizer is a phosphonate based admixture, or a polycarboxylate ether based admixture.

8. The process according to claim 7, wherein the dry premix comprises 0.5-10 wt-% of a polycarboxylate ether based superplasticizer

9. The process according to claim 7, wherein the polycarboxylate ether based superplasticizer has a charge density of >1.5 meq/g.

10. The process according to claim 7, wherein the dry premix comprises 0.5-10 wt.-% of a phosphonate based superplasticizer.

11. The process according to claim 1, wherein a polyether is used as said defoaming agent.

12. The process according to claim 11, wherein the dry premix comprises 0.05-2 wt.-% of a polyether based defoaming agent.

13. The process according to claim 6, wherein the stabilizing agent is a diutan gum.

14. The process according to claim 6, wherein the dry premix comprises 0.2-2 wt.-% of the stabilizing agent.

15. The process according to claim 1, wherein the mine tailings have a solid content of 70-82 wt-%.

16. The process according to claim 1, wherein the mine tailings are from a mine extracting at least one of gold, silver, copper, zinc, uranium, platinum, palladium, nickel, beryllium, cobalt, chromium, gallium, indium, lead, lithium, magnesium, manganese, molybdenum, aluminium, barium, antimony, bismuth, tantalum, titanium, tungsten, vanadium, zinc, iron, diamonds, sapphires, opals, emeralds, rubies, graphite, alexandrite, aquamarines, spinel, topaz, cadmium, potash, molybdenum, a rare earth element and a platinum group metal

17. The process according to claim 1, wherein the solids content of the backfill material is 74-80 wt.-%.

18. The process according to claim 5, wherein the amount of dry premix is selected so that the backfill material has a content of Portland cement of 2-14 wt.-%.

19. The process according to claim 5, wherein the amount of dry premix is selected so that the backfill material has a content of hydraulic binder of 3-6 wt.-%.

20. The process according to claim 8, wherein the dry premix comprises 1-6 wt.-% of a polycarboxylate ether based superplasticizer.

Description

EXAMPLES

[0043] The present invention will now be illustrated in more detail by reference to the following examples.

Materials

[0044] The following notation is used to describe the samples used in the following examples: [0045] C4-CEM III-PD 78-Br5-PCP1 4.5

Where:

[0046] C4 is the tailings sample [0047] CEM III is the hydraulic binder [0048] PD is the solids content (also referred to as pulp density) (weight %) [0049] Br is the binder content (weight %) [0050] PCP1 is a superplasticizer [0051] 4.5 is the amount of PCP1 (weight % in the binder

[0052] The pulp density corresponds to the percentage of solids fractions in the backfill material.

[0053] Several types of admixtures have been tested with various dosages: [0054] PCP1 to PCP5 are various superplasticizers, described in detail in the table below, [0055] PE1 is a polyether used as defoaming agent, [0056] DG1 is a diutan gum used as stabiliser, [0057] PN1 is a phosphonate used as a superplasticizer.

TABLE-US-00001 Solid Charge Chemical content density Function nature Form (wt.-%) (meq/g) PE1 Defoaming Polyether Powder 100 N.A. agent PN1 Plasticizer Diphosphonate Liquid 30 N.A. PCP1 Plasticizer Methacrylic Liquid 20 1.1 Polycarboxylate ether PCP2 Plasticizer Cationic Liquid 50 N.A. polymer PCP3 Plasticizer Methacrylic Liquid 20 1.6 Polycarboxylate ether PCP4 Plasticizer Polycarboxylate Powder 100 1.55 ether PCP5 Plasticizer Polycarboxylate Powder 100 1.86 ether

[0058] Several types of tailings were tested: [0059] Can1,are tailings coming from a zinc mine in Canada. [0060] Mal1,are tailings coming from a gold mine in Mali. [0061] DRC1 are tailing coming from a gold mine in DRC. [0062] C4 is a siliceous filler that has a similar particle size distribution than common tailings.

Process of Preparation of Cemented Paste Backfills

[0063] In laboratory, for examples 1 to 4, the cemented paste backfill samples were prepared according to the following procedure: [0064] Mine tailings, the dry premix of the invention and water are poured into in a 2-litre bowl of a mortar mixer. [0065] The mixer is started at low speed (50 rpm) and within the first 30 seconds all the mixing water is added. [0066] After 5 minutes of mixing the mixer is stopped.

[0067] For examples 5 and 6, cemented paste backfill samples were made with a concrete mixer according to the same mixing procedure. This concrete mixer was equipped with a 20 litres bowl. 10 litres (around 20 kg) of cemented paste backfill was mixed.

Measurement Methods

[0068] For examples 1 to 4, fluidity of the paste was measured just after mixing and at various testing times after mixing (up to 2 hours) with a methyl methacrylate (MMA) cone of 20 mm upper diameter, 40 mm lower diameter and 58 mm height. Its total volume is 40.3 mL. The cone is shown in FIG. 1.

[0069] The cone was filled in with a single layer of cemented paste backfill. The paste was cut at the top surface with a spatula then the cone was lifted and the material was allowed to spread onto a slightly wet glass plate.

[0070] The diameter of the backfill was measured in millimetres on two diameters after stabilization of the spreading. The resulting flow value is the main value of the two measurements.

[0071] For example 5, the Abrams cone (100/200 mm diameter, 300 mm height) test was used to follow the evolution of fluidity of the paste as function of time.

[0072] Unconfined Compressive Strength has been measured on undrained 5×5×5 cm cemented paste backfill cubes at various testing ages. The moulds were filled with a single layer of cemented paste backfill. The top surface of the paste was cut and smoothed. Cubes were cured in moulds at 35° C. and 100% relative humidity until the testing ages. Samples were broken at a rate of compression of 2 mm/min.

[0073] The charge density of the polycarboxyies is defined as the number of charges present on the polymer. This number is expressed in meq/g, corresponding as the moles of charges per gram of polymer in the superplasticizer.

[0074] The charge density is here measured by electrometric titration, using an automatic titration device: Titrando 808, Dosino 800 and stirrer 801, supplied by Metrohm. The software Tiamo from Metrohm is used to carry out the measurement and process the measured data in order to calculate the charge density.

[0075] To measure the charge density, two consecutive titrations are required; a first one with a strong acid, such as chloric acid, and another with a strong base, such as sodium hydroxide. The purpose of the first titration is to make sure that ail the charges of the polymer are protonated. The second titration enables to determine the equivalence points used for the calculation of the charge density.

[0076] The following experimental protocol is used: [0077] A mixture of 10 g of superplasticizer is added to a beaker, and diluted with 70 mL of deionised water, [0078] The mixture is continuously stirred using a magnetic bar and stirrer, [0079] The pH electrode, calibrated prior to the measurement, is placed into the solution and continuously measures the pH, [0080] A solution of chloric acid 0.1N+/−0.2% is slowly added to the mixture and the pH is measured as a function of the volume of said solution added, [0081] A solution of sodium hydroxide 0.1N+/−0.2% is slowly added to the mixture and the pH is measured as a function of the volume of said solution added.

[0082] The titration device then computes the charge density of the polymer by plotting the measured pH as a function of the volume of sodium hydroxide, and determining the two equivalence points V.sub.e1 and V.sub.eq2. The charge density is finally calculated using software Tiamo, using the following mathematical formulae:

[00001]$\mathrm{CD}=\left[\mathrm{NaOH}\right].Math.\left(V_{\mathrm{eq}2}-V_{\mathrm{eq}1}\right)/M_{\mathrm{PCP}}$

Where: CD is the charge density (in meq/g), [0083] [NaOH] is the concentration of sodium hydroxide in the solution added (in mol/L), [0084] V.sub.eq1 and V.sub.eq2 are the two equivalence points (in L), [0085] M.sub.PCP is the weight of polycarboxylate in the superplasticizer (in g of dry polymer).

EXAMPLE 1

Flow of Reference Backfill Materials

[0086] Without any admixture being used, backfill materials made of C4 or tailings Can1 or Mal1 have low flow values.

TABLE-US-00002 Flow (mm) Sample after 120 min C4 - CEM III - PD78 - Br 5 40 Can1 - CEM III - PD74 - Br 5 50 Mal1 - CEM III - PD80 - Br 5 50

EXAMPLE 2

Flow of Backfill Materials with Plasticizers, without Any Stabiliser

[0087] The best flow is obtained with PCP admixtures, at a dosage of 3.5 wt.-% of the amount of binder, here a CEM III. The phosphonate admixture PN1 requires higher dosages to be effective, i.e. 2.5 wt.-%.

[0088] From this example, PCP1 is a preferred admixture.

TABLE-US-00003 Flow (mm) Sample after 120 min C4 - CEM III - PD78 - Br 5 (reference) 40 C4 - CEM III - PD78 - Br 5 - PCP1 at 1.2 wt.-% 70 C4 - CEM III - PD78 - Br 5 - PCP1 at 3.5 wt.-% 150 C4 - CEM III - PD78 - Br 5 - PN1 at 1.2 wt.-% 40 C4 - CEM III - PD78 - Br 5 - PN1 at 2.5 wt.-% 40 C4 - CEM III - PD78 - Br 5 - PN1 at 3.5 wt.-% 100

EXAMPLE 3

Flow of Backfill Materials with Plasticizers and with a Stabiliser

[0089] The addition of PCP4 at 1 wt.-% and DG1 at 0.5 wt.-% is enough to multiply the flowability by more than two, while a mixture of 4.5 wt.-% PCP2 and 10 wt.-2 PCP3 and 0.5 wt.-% DG1 results in only twice the flowability when compared to the reference. PCP4 alone is able to achieve a better performance than the combination of PCP2 and PCP3. From this example, PCP4 is preferred over PCP2 and PCP3 for this invention.

TABLE-US-00004 Flow (mm) Sample after 120 min Can1 - CEM III - PD74 - Br 5 (reference) 50 Can1 - CEM III - PD74 - Br 6 - 100 PCP2 4.5 - PCP3 10 - DG1 0.5 Can1 - CEM III - PD75 - Br5 - 120 PCP4 1 - DG1 0.5

EXAMPLE 4

Flow of Backfill Materials with Various Admixtures

[0090] With 2.5 wt.-% PCP5 the flowability of the cemented paste backfill material is multiplied by nearly three. The addition of 0.1 wt.-% PE1 further improves the flow.

[0091] This example shows that polycarboxylate ether based plasticizers are particularly suitable for the invention, used alone. The addition of a defoaming agent further increases the flow.

[0092] The addition of PCP increases the amount of entrained air in the cemented paste backfill material and penalizes mechanical performances. PE1 is a defoaming agent added to limit this negative effect. It is, however, surprising that the addition of a defoaming agent increases the flowability, since entrained air usually promotes flowability so that it would have been expected that the addition of the defoaming agent has a negative effect on flowability.

TABLE-US-00005 Flow (mm) Sample after 120 min Mal1 - CEM III - PD80 - Br 5 (reference) 50 Mal1 - CEM III - PD80 - Br 5 PCP5 2.5 wt.-% 130 Mal1 - CEM III - PD80 - Br 5 PCP5 2.5 wt.-% - 140 PE1 0.1 wt.-% Mal1 - CEM III - PD80 - Br 5 PCP5 2.0 wt.-% 110

EXAMPLE 5

Evolution of Flow Over Time

[0093] The flowability of the cemented paste backfill material as a function of time decreases, as shown in FIG. 2. However, the addition of PCP5 improves the flow sufficiently to allow the transportation of the cemented paste backfill material for a duration of 120 minutes.

[0094] PCP 5 is therefore particularly suitable for this invention. It is assumed that the high charge density of PCP 5 contributes to the increased flowability.

Example 6

Impact of the Admixtures on Mechanical Properties of Backfills

[0095] The addition of PCP5 and PEI significantly improves the mechanical strength at both early and medium terms while PCP4 does not improve strength, as shown in FIG. 3.