USE OF LEAD SMELTING SLAGS FOR THE STABILIZATION OF METAL IONS FROM SOLID OR LIQUID MEDIA

Abstract

A method of treating, stabilizing, precipitating, or otherwise removing heavy metal ions contained in a contaminated media, which method includes: providing a sodium-iron-sulfide mineral or crystalline phase, either alone or in combination with a pH adjusting substance; contacting said contaminated media containing heavy metal ions with the sodium-iron-sulfide mineral or crystalline phase, either alone or in combination with a pH adjusting substance; and allowing the contaminated media containing the heavy metal ions to react with said sodium-iron-sulfide mineral or crystalline phase, either alone or in combination with a pH adjusting substance, such that the contaminated media containing heavy metal ions form single or mixed metal-sulfide precipitates or co-precipitates.

Claims

1. A method of treating, stabilizing, precipitating, or otherwise removing heavy metal ions contained in a contaminated media, which method comprises the steps of: providing a sodium-iron-sulfide mineral or crystalline phase, either alone or in combination with a pH adjusting substance; contacting said contaminated media containing heavy metal ions with the sodium-iron-sulfide mineral or crystalline phase, either alone or in combination with a pH adjusting substance; and allowing the contaminated media containing the heavy metal ions to react with said sodium-iron-sulfide mineral or crystalline phase, either alone or in combination with a pH adjusting substance, such that the contaminated media containing heavy metal ions form single or mixed metal-sulfide precipitates or co-precipitates.

2. The method of treating stabilizing, precipitating, or otherwise removing heavy metal ions contained in a contaminated media according to claim 1, wherein the sodium-iron-sulfide mineral or crystalline phase is comprised of Na.sub.3Fe.sub.2S.sub.4, NaFeS.sub.2, or NaFeS.sub.2:xH.sub.2O, where x2.

3. The method of treating stabilizing, precipitating, or otherwise removing heavy metal ions contained in a contaminated media according to claim 2, wherein the Na.sub.3Fe.sub.2S.sub.4, NaFeS.sub.2, or NaFeS.sub.2:xH.sub.2O, where x2 is obtained from a slag or industrial byproduct.

4. The method of treating, stabilizing, precipitating, or otherwise removing heavy metal ions contained in a contaminated media according to claim 3, wherein the Na.sub.3Fe.sub.2S.sub.4, NaFeS.sub.2, or NaFeS.sub.2:xH.sub.2O, where x2 is obtained from a slag or industrial byproduct generated during lead smelting.

5. The method of treating stabilizing, precipitating, or otherwise removing heavy metal ions contained in a contaminated media according to claim 1, wherein the contaminated media containing heavy metal ions contains at least one heavy metal from a group consisting of antimony, arsenic, cadmium, chromium, cobalt, copper, lead, manganese, mercury, nickel, palladium, platinum, selenium, silver, thallium, tin, or zinc.

6. The method of claim 1, wherein the pH adjusting substance comprises an acid.

7. The method of claim 1, wherein the pH adjusting substance comprises a base.

8. The method of claim 1, wherein the contaminated media is contacted with the sodium-iron-sulfide mineral or crystalline phase either simultaneously with of after the contaminated media is contacted with a pH adjusting substance.

9. A method of treating, stabilizing, precipitating, or otherwise removing heavy metal ions contained in a solid, sludge, soil, suspension, or sediment, which method comprises the steps of: providing a sodium-iron-sulfide mineral or crystalline phase, either alone or in combination with a pH adjusting substance; contacting said solid, sludge, soil, suspension, or sediment containing heavy metals with the sodium-iron-sulfide mineral or crystalline phase, either alone or in combination with a pH adjusting substance; and allowing the solid, sludge, soil, suspension, or sediment containing the heavy metal ions to react with said sodium-iron-sulfide mineral or crystalline phase, either alone or in combination with a pH adjusting substance, such that the solid, sludge, soil, suspension, or sediment containing heavy metal ions form single or mixed metal-sulfide precipitates or co-precipitates and render the thus treated solid, sludge, soil, suspension, or sediment containing heavy metals non-hazardous.

10. The method of treating, stabilizing, precipitating, or otherwise removing heavy metal ions contained in a solid, sludge, soil, suspension, or sediment according to claim 9, wherein the sodium-iron-sulfide mineral or crystalline phase is comprised of Na.sub.3Fe.sub.2S.sub.4, NaFeS.sub.2, or NaFeS.sub.2:xH.sub.2O, where x2.

11. The method of stabilizing, precipitating, or otherwise removing heavy metal ions contained in a solid, sludge, soil, suspension, or sediment according to claim 10, wherein the Na.sub.3Fe.sub.2S.sub.4, NaFeS.sub.2, or NaFeS.sub.2:xH.sub.2O, where x2 is obtained from a slag or industrial byproduct.

12. The method of stabilizing, precipitating, or otherwise removing heavy metal ions contained in a solid, sludge, soil, suspension, or sediment according to claim 11, wherein the Na.sub.3Fe.sub.2S.sub.4, NaFeS.sub.2, or NaFeS.sub.2:xH.sub.2O, where x2 is obtained from a slag or industrial byproduct generated during lead smelting.

13. The method of treating, stabilizing, precipitating, or otherwise removing heavy metals contained in a solid, sludge, soil, suspension, or sediment according to claim 9, wherein the solid, sludge, soil, suspension, or sediment containing heavy metal ions contains at least one heavy metal from a group consisting of antimony, arsenic, cadmium, chromium, cobalt, copper, lead, manganese, mercury, nickel, palladium, platinum, selenium, silver, thallium, tin, or zinc.

14. The method of claim 9, wherein the pH adjusting substance comprises an acid.

15. The method of claim 9, wherein the pH adjusting substance comprises a base.

16. The method of claim 9, wherein the solid, sludge, soil, suspension, or sediment is contacted with the sodium-iron-sulfide mineral or crystalline phase either simultaneously with of after the solid, sludge, soil, suspension, or sediment is contacted with a pH adjusting substance.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will be described with reference to the attached drawings which are given as non-limiting examples only, in which:

[0026] FIG. 1 depicts the solubility of selected metal hydroxides and sulfides as a function of pH.

DETAILED DESCRIPTION OF THE DRAWINGS AND THE PRESENTLY PREFERRED EMBODIMENTS

[0027] The present invention provides a methods for the use of various sodium-iron-sulfide mineral (or crystalline) phases contained in slags generated during lead smelting processes for the treatment, stabilization, precipitation, or otherwise removal of heavy metal pollutants contained in contaminated media.

[0028] Herein, the term contaminated media means media, including but not limited to, solids, sludges, soils, suspensions, sediments, aquifers (particularly groundwater), industrial process or wastewaters that contain heavy metal contaminants or pollutants.

[0029] Slags obtained from lead smelting processes and in particular those slags obtained from processes using sodium alkali fusion are highly variable. This variability in the slag composition is the result of a combination of parameters, including but not limited to the lead paste feedstock composition, smelting furnace operation (e.g. temperature; type of alkali used), atmospheric exposure of the slag both during and after its formation, and environmental conditions during slag storage and aging. As a result, any particular sodium-iron-sulfide slag may contain, in addition to other contaminants, varying combinations of Na.sub.3Fe.sub.2S.sub.4, NaFeS.sub.2, and NaFeS.sub.2:xH.sub.2O where x2.

[0030] The proposed disassociation reactions for NaFeS.sub.2 and NaFeS.sub.2:2H.sub.2O are:

NaFeS.sub.2+0.875H.sup.++0.5H.sub.2ONa.sup.++Fe.sup.2++1.875HS.sup.+0.125SO.sub.4.sup.2 (1)

NaFeS.sub.2:2H.sub.2O+0.875H.sup.+Na.sup.++Fe.sup.2++1.875HS.sup.+0.125SO.sub.4.sup.2+1.5H.sub.2O (2)

[0031] Based on these reactions and the solubility products (Ksp) referenced in Table 1, when a slag containing NaFeS.sub.2 and/or NaFeS.sub.2:2H.sub.2O is introduced to a contaminated media containing a number of heavy metal ions, the NaFeS.sub.2 and/or NaFeS.sub.2:2H.sub.2O (which have relatively high solubility products) will preferentially disassociate to form metal-sulfide precipitates with lower solubility products.

[0032] In addition to the sulfide ions (S.sup.2) generated during the preferential disassociation reactions of NaFeS.sub.2 or NaFeS.sub.2:2H.sub.2O to form single metal-sulfide precipitates with lower solubility products, these same disassociation reactions concurrently generate iron ions (Fe.sup.2+) which, when combined with other heavy metals, may form mixed metal-sulfide precipitates (e.g. FeAsS, CuFeS.sub.2, FeSb.sub.2S.sup.4) of lower solubility.

[0033] Careful consideration of the overall stoichiometry and mixture composition is required to both economically and effectively treat contaminated media since the precipitation of a lower solubility metal-sulfide may occur as the result of the disassociation of a more readily soluble metal-sulfide. In some cases, the lowering of the dissolved (or leachable) level of a hazardous metal pollutant in a contaminated media to below a regulatory goal may elevate the dissolved (or leachable) level of a different hazardous metal pollutant to a concentration greater than its respective regulatory goal.

[0034] For example, if NiS, is already present in the contaminated media (or in the sodium-iron-sulfide slag, it may disassociate in the presence of dissolved Pt in the contaminated media to be treated. Depending upon the stoichiometry and other factors (e.g. pH, temperature, oxidation-reduction potential), the formation of PtS may result in the lowering the dissolved Pt concentration to a desired regulatory goal, but increase the dissolved (or leachable) Ni concentration to unacceptable levels.

[0035] One method to mitigate this aforementioned quandary of solving one problem while creating another may be to design the overall treatment methodology such that multiple treatment methods or protocols are used simultaneously or sequentially.

[0036] An example where multiple treatment methods are used would be to treat a contaminated solid waste with a mixture of a base (e.g. CaO, Ca(OH).sub.2) and a sodium-iron-sulfide slag, either sequentially or in combination.

[0037] An example of a sequential treatment method would be to remove of a specific heavy metal pollutant from an industrial waste water by pH adjustment to promote metal-hydroxide precipitation followed by the use of a sodium-iron-sulfide slag to remove the remaining heavy metal pollutants in the effluent as metal-sulfide precipitates. The pH may be adjusted upward or downward by use of a variety of bases (e.g. CaO, Ca(OH).sub.2, NaOH) or acids (HCl, H.sub.2SO.sub.4, H.sub.3PO.sub.4) as required to achieve a particular treatment goal.

[0038] These types of treatment protocols, where multiple treatment methods are used simultaneously or sequentially, either continuously or by a batch process are typical in both hazardous solid waste treatment facilities and industrial wastewater treatment plants.

[0039] The present invention will be discussed with reference to the following non-limiting examples which are to be considered merely representative of the present invention and, thus, should not be considered as limiting.

[0040] Table 2 summarizes below various treatment of two untreated electric arc furnace dust waste streams (EAF #1; EAF #2) and a third untreated dust stream from an argon oxygen decarburization (AOD) process at a stainless steel facility. Each waste stream has exceedances of maximum LDR concentration for various combinations of cadmium, chromium, lead, and zinc. (e.g. Samples #1, #2, and #27).

TABLE-US-00002 TABLE 2 Treatment of EAF Dust Sample Waste NaFeS TCLP Maxmum LDR Leachable Concentration (mg/L) No. ID % wt pH ORP (mv) As Cd Cr Ni Pb Sb Se Zn 5.0 0.11 0.60 11 0.75 1.15 5.7 4.3 EAF and AOD Controls 1 EAF #1 5.78 +168.8 0.009 1.585 1.043 8.911 0.076 0.017 0.191 101.58 2 EAF #2 7.13 +60.6 0.030 0.050 0.002 4.472 0.623 0.432 0.014 34.22 27 AOD 12.66 161.2 0.011 ND 11.21 ND 8.584 0.130 0.018 1.864 EAF + 20% AOD (wt/wt) 11 EAF #1 11.09 100.1 0.010 0.001 0.835 0.014 0.075 0.025 0.114 0.279 12 EAF #2 11.55 105.5 0.016 ND 0.844 0.044 2.872 0.024 0.009 0.925 10% LIME (wt/wt) 31 EAF #1 10.81 55 0.004 ND 0.114 0.020 0.021 0.012 0.125 0.089 32 EAF #2 11.88 87 0.037 ND 0.019 0.035 5.816 0.035 ND 0.664 5% (NaFeS), (wt/wt) 29 EAF #1 5% 6.03 157.7 ND 0.008 0.222 7.119 0.039 0.040 0.090 24.545 30 EAF #2 5% 7.62 283.2 0.016 ND 0.002 0.441 0.017 0.358 0.003 0.197 28 AOD 5% 12.62 528.2 0.006 ND 0.004 ND 0.008 ND ND 0.045 10% LIME + (NaFeS) 3 EAF #1 5% 11.67 130.7 0.007 ND 0.004 0.023 0.007 0.008 0.140 0.069 4 EAF #1 10% 11.92 259.7 ND 0.009 0.034 ND ND 0.129 5 EAF #2 5% 12.41 280.8 0.014 ND 0.008 0.039 0.006 0.001 0.004 0.068 6 EAF #2 10% 12.38 461.1 0.038 ND 0.007 0.016 0.004 0.001 0.023 0.088 20% AOD + (NaFeS) Slag #28 EAF #1 5% 11.41 177.3 0.009 ND 0.014 0.030 0.006 ND 0.094 0.074 Slag #28 EAF #1 10% 11.27 184.2 0.001 ND 0.003 0.011 0.005 ND 0.088 0.055 Slag #28 EAF #2 5% 11.91 180.6 0.016 ND 0.003 0.026 0.005 0.015 0.003 0.048 Slag #28 EAF #2 10% 11.91 265.1 0.016 ND 0.003 0.017 0.007 ND 0.010 0.028 Slag #60 EAF #1 5% 11.20 167.0 0.007 ND 0.004 0.014 0.008 ND 0.112 0.036 Slag #60 EAF #2 5% 11.62 211.0 0.010 ND 0.002 0.037 ND 0.021 0.016 0.038 Slag #75 EAF #1 5% 11.14 270.1 ND ND 0.002 0.008 0.005 ND 0.097 0.034 Slag #75 EAF #2 5% 11.69 272.9 0.009 ND 0.002 0.030 ND 0.027 0.008 0.032

[0041] Again in referring to Table 2, as an alternative to virgin lime addition to raise the pH, a 20% (wt/wt) addition of AOD was mixed with EAF #1 or EAF #2 to raise the pH to 10.81 and 11.88, respectively. Although EAF #1 was successfully treated for cadmium and zinc, the treatment protocol was unsuccessful in meeting the maximum LDR concentration for chromium (Sample #11). Further, the treatment of EAF #2 resulted in successfully treating for zinc, however LDR concentration exceedances for chromium and lead remained (Sample #12).

[0042] Again in referring to Table 2, a 10% (wt/wt) lime addition to EAF #1 to promote metal-hydroxide precipitation was successful in achieving compliance for cadmium, chrome, and zinc (Sample #31). The same 10% (wt/wt) lime addition treatment to EAF #2 resulted in the successful treatment of zinc however simultaneously created an LDR concentration exceedance for lead (Sample #32).

[0043] Again in referring to Table 2, when either EAF #1, EAF #2, or AOD was treated with a 5% (wt/wt) addition of a secondary lead smelting slag containing a sodium-iron-sulfur mineral or crystalline phase as described in the present invention, treatment of EAF #2 and the AOD was successful (Samples #30 and #28), however treatment of EAF #1 was still unsuccessful in meeting the maximum LDR concentration for zinc (Sample #29).

[0044] Again in referring to Table 2, various combinations of 10% lime addition plus, 5% or 10% (wt/wt) addition of a secondary lead smelting slag containing a sodium-iron-sulfur mineral or crystalline phase as described in the present invention were all successful in treating EAF #1 and EAF #2 (Samples #3 through #6).

[0045] The remaining data in Table 2 represents successful compliance for maximum LDR concentration for all metals in two electric arc furnace dusts (EAF #1 or EAF #2) by a mixture of 20% (wt/wt) AOD, plus a 5% or 10% (wt/wt) addition of various secondary lead smelting slags (Slag #28, Slag #60, and Slag #75) each containing a sodium-iron-sulfur mineral or crystalline phase as described in the present invention.

[0046] Table 3 below summarizes various treatment protocols tested on a chromite ore processing residue. Chromite ore processing residue (COPR) is a waste byproduct of chromate production that contains high levels of total chromium and hexavalent chromium (Cr[VI]). In the COPR samples tested here, the hexavalent chromium concentrations averaged between 5,660 and 7,220 mg/kg with TCLP chromium averaging 320 to 349 mg/L.

TABLE-US-00003 TABLE 3 Treatment of Chromite Ore Processing Residue (COPR) TCLP Cr Treatment (mg/L) LDR Maximum Concentration 0.60 COPR - untreated.sup.(*.sup.) 320 to 348.8 COPR - treated with: 14% Lime 91.37 14% Lime + 2.5% NaHS 27.696 14% Lime + 5% NaHS 4.301 14% Lime + 5% NaFeS Slag 0.896 14% Lime + 10% NaFeS Slag 0.010 14% Lime + 15% NaFeS Slag 0.057 15% NaFeS Slag 0.034 .sup.(*.sup.)The untreated COPR sample had a hexavalent chromium concentration of 5,660 to 7,220 mg/kg.

[0047] The results summarized in Table 3 indicate that treatment of the COPR with 14% lime addition (wt/wt), 14% lime addition+NaHS, or a 14% lime addition+5% of a secondary lead smelting slag containing a sodium-iron-sulfur mineral or crystalline phase as described in the present invention were not able to lower the TCLP chromium concentration below the maximum LDR chromium limit of 0.60 mg/L.

[0048] Although a 14% lime addition plus either NaHS or 5% secondary lead smelting slag was not apparently successful at the above mentioned dose rates, either alone or in combination, treatment of the same COPR sample with a 10% or 15% by weight secondary lead smelting slag containing a sodium-iron-sulfur mineral or crystalline phase as described in the present invention (with or without a 14% lime addition) were successful in lowering the TCLP chromium concentration below the maximum LDR chromium limit of 0.60 mg/L.

[0049] The results of these tests demonstrate that the use a secondary lead smelting slag containing a sodium-iron-sulfur mineral or crystalline phase as described in the present invention provides for the stabilization of heavy metal pollutants from contaminated media.

[0050] The simultaneous re-use one industrial waste (slag) to treat another contaminated media as described in the present invention is also economical (use of waste byproducts compared to virgin treatment chemicals) and overcomes the actual or potential safety and handling drawbacks of other known sulfide treatment technologies (use of NaHS).

[0051] Although the present invention has been described with reference to particular means, materials and embodiments, from the foregoing description, one skilled in the art can easily ascertain the essential characteristics of the present invention and various changes and modifications can be made to adapt the various uses and characteristics without departing from the spirit and scope of the present invention as described above and set forth in the attached claims.