The producing of lead and elemental sulfur by new technologies from galenite ores.
A major cost factor in the sintering and smelting process for producing Pb is the control needed to meet existing environmental standards for Pb emissions. Another issue is the current concern over acid rain, which will in all probability result in even more stringent controls on emission of sulfur gases.
Processing of the galena mixtures or concentrates is developed as an effective low-temperature leaching-electrowinning method to produce Pb metal and elemental sulfur from galena mixtures or concentrates. The method reduces Pb emissions and totally eliminates the formation of sulfur gases. The elemental S produced is more economical to store and ship than the sulfuric acid ([H.sub.2]S[O.sub.4]) generated by the high-temperature smelting process.
This hydrometallurgical method consists of leaching galena synthetic mixtures or concentrates in waste fluosilicic acid ([H.sub.2] [SiF.sub.6]) with hydrogen peroxide ([H.sub.2] [O.sub.2]) and lead dioxide (Pb[O.sub.2]) as oxidants at 95[degrees], electrowinning the ([PbSiF.sub.6]) solution at 35[degrees] to produce 99,99% Pb metal, and solvent extraction to recover S, leaving a residue containing eventually present Cu, Ag, and other metal values.
2PbS+3[H.sub.2] Si[F.sub.6]+[H.sub.2][0.sub.2]+ Pb[0.sub.2][??]
Several galena leaching process have been investigated, including processing using ferric chloride, ferric sulfate, nitric acid and ammonium acelate solutions. The leached Pb[Cl.sub.2] and PbS[O.sub.4] salts have a very limited solubility in aqueous solution, making aqueous electrolysis difficult. Lead metal was recoverable from Pb[Cl.sub.2] by molten-salt electrolysis operated at 450[degrees]. It is known that electrowinning of Pb in HN[O.sub.3] and [H.sub.2]Si [F.sub.6] solutions yields Pb metal at the cathodes and at the same time Pb[O.sub.2] at the anodes.
The next text will explain the oxidative leaching-electro-winning process. The parameters for leaching process about synthetic mixtures were investigated in laboratory experiments.
The chemical equations for PbS leaching in acid solution with and without oxidants are following:
Reaction (3) shows that oxidative leaching of PbS will yield Pb salt and elemental S. Reaction (4) suggests PbS[O.sub.4] may form if the redox potential of the solution is too high, and reaction (5) indicates [H.sub.2]S will form when leaching in acid solution if the redox potential is too low. To avoid the generation of [H.sub.2]S one-fourth of the required oxidant have to be added to the [H.sub.2]Si[F.sub.6] solution prior to the addition to the PbS. The reaction is exothermic and it is necessary to add [H.sub.2] [O.sub.2] slowly to avoid overheating the leach solution. After adding the [H.sub.2] [O.sub.2], Pb[O.sub.2] was added slowly to control the redox potential. The reactions occurring during the oxidative leaching of PbS synthetic mixtures or concentrates with [H.sub.2]Si[F.sub.6] are shown below.
PbS+[H.sub.2][0.sub.2]+[H.sub.2]Si[F.sub.6][??]PbSi[F.sub.6]+2[H.sub.2] 0+[S.sup.o] (6)
PbS+Pb[0.sub.2]+[H.sub.2[Si[F.sub.6][??]PbSi[F.sub.6]+Pb0+[H.sub.2]0+ [S.sup.o] (7)
At the end of leaching, the mixture was filtered to separate the leachate from the residue. The residue consisted of elemental S and other metal values. The leachate is sent to electrowinning to recover pure Pb metal.
As leaching parameters were investigated: PbS samples of 98% on the 400 mesh or 96% on the as-received concentrates if [H.sub.2]S[O.sub.2] and Pb[O.sub.2] were used as oxidants (the possible oxidants may be air, oxygen, ozone, HN[O.sub.3] and Mn[O.sub.2]); leaching temperature from 50-95[degrees]; leaching time from 35-335 min. The results of carried out investigations are shown in Tables 1-4.
The effect of using different combinations of oxidants of [H.sub.2]S[O.sub.2] and Pb[O.sub.2] on PbS leaching was insignificant. Previous leaching experiments showed that [H.sub.2]S[O.sub.2] was a more efficient oxidizer to initiate the leach reaction. Also, it was less expensive than Pb[O.sub.2]. Thus, it is beneficial to use [H.sub.2]S[O.sub.2] to leach PbS and only use Pb[O.sub.2] at the end of the leach to void oxidizing PbS into PbS[O.sub.4].
Leaching temperatures had a great influence on reaction rate and Pb extraction. When leaching below 80[degrees]C, the reaction rate was thought to be too slow for any practical application. Lead extraction was 96% when leaching at 95[degrees]C for 35 min using [H.sub.2]S[O.sub.2] and Pb[O.sub.2] as oxidants. The leaching rate increased greatly and the required leaching time was reduced from 90 min to 35 min as the temperature increased from 90[degrees]C to 95[degrees]C. Lead extraction was increased from 92% to 96% as leaching time increased from 30 min to 60 min at 95[degrees]C. initial leaching was rapid, but the elemental sulfur formed and coated the PbS particles, further reaction was probably diffusion controlled and the leach rate was reduced. However, the effect of the sulfur coating was not critical, because of the fine particle size of the PbS.
The amounts of PbS, Pb[O.sub.2] and [H.sub.2[Si[F.sub.6] used in a leach test determined the concentration of PbSi[F.sub.6] and free [H.sub.2[Si[F.sub.6] in the pregnant leachate. Increasing the concentration of free [H.sub.2[Si[F.sub.6] above 60 g/lit had no significant effect on the Pb extraction, extraction of impurities decreased with decreasing concentration of free [H.sub.2[Si[F.sub.6].Lead extraction of 96%, 91% and 96% were achieved using [H.sub.2[Si[F.sub.6] solutions made from technicalgrade, waste, and recycled acid. Waste [H.sub.2[Si[F.sub.6] contained HCl and [H.sub.2]S[O.sub.4] as impurities, which formed some insoluble Pb salts during leaching, resulting in lower Pb extraction. Recycled electrolyte, in which impurities were removed during prior leaching, was as reactive as technical-grade [H.sub.2[Si[F.sub.6].
The conditions by the leaching process of the synthetic galena mixtures (PbS) with gangue mineral's compounds (ZnS, CuS, NiS, CoS, CaO, MgO, [Fe.sub.2][O.sub.3], Si[O.sub.2]) and oxidants addition [H.sub.2]S[O.sub.2] and Pb[O.sub.2], leaching temperature ([degrees]C) with retaining leaching time (min) in the presence of technical [H.sub.2[Si[F.sub.6] are shown in the Tables 5-8.
Above mentioned combined hydrometallurgical and electrometallurgical methods are developed to produce lead and elemental S from synthetic mixtures or concentrates with high purity. Contemporary, this process eliminates S gases and Pb emissions. The elemental S produced is easier to transport and store than is the [H.sub.2]S[O.sub.4] generated by the pyrometallurgical methods.
Investigated experiments and tests included oxidative leaching of PbS in synthetic mixtures with [H.sub.2[Si[F.sub.6], electrowinning the leach solution to produce high-purity lead metal, carbon treatment of spent electrolyte for recycling, and S removal from the leach residue. investigated experiments by PbS synthetic mixtures show satisfactory Pb extraction and appropriate possibility for treatment of natural ore samples and concentrates produced in industrial mineral processing lead-zinc plants in the Republic of Macedonia.
Cole, E., 1985. Production of lead from sulfides, U.S. pat. 4500398.
Cole, E., 1985. "Update on recovering lead from scrap batteries," Journal Metall., Vol. 37, pp. 79-83.
Cole, E., 1985. "Recovery of lead from battery sludge," Journal Metall., vol.35, pp42-46.
Haver, F., 1970. "Recovery of lead and sulfur from galena concentrate using a ferric sulfate leach," u.S. BuMines Ri 7360, pp.13.
Lee, A., 1984. "Electrolytic method for recovery of lead from scrap batteries," U.S. BuMines RI 8857, pp.20.
Lee, A., 1986. "Hydrometallurgical process for producing lead and elemental sulfur from galena Concentrates," BuMines Ri 9055, pp.13.
Wong, M., 1983. "integrated operation of ferric chloride leaching, Molten-Sat Electrolysis Process for Production of Lead," U.S. BuMines RI 8770, pp.21.
Faculty of Natural and Technical Sciences
"Goce Delcev" University, Macedonia
ALEXANDAR KRSTEV, DEJAN KRSTEV
Faculty of informatics
"Goce Delcev" University, Macedonia
TABLE 1. EFFECT OF VARIOUS AMOUNTS OF OXIDANTS Test [H.sub.2] Pb[O.sub.2], Pb, [O.sub.2]35%, gr. % ml 1 0.0 16.0 92.0 2 2.5 17.0 95.0 3 5.0 9.8 95.0 4 7.5 8.1 96.8 5 10.0 5.7 95.1 6 19.0 0.0 96.0 TABLE 2.EFFECT OF TIME AND TEMPERATURE Leach Leach time, Pb,% temperature, min T [degrees]C 50 335 62.3 70 240 91.5 80 90 76.0 90 75 90.1 90 90 97.5 95 35 96.0 95 75 96.5 TABLE 3. EFFECT OF LEACH TIME IN PB EXTRACTION Leach time 30 min 60 min 90 min Pb% 92.3 95.6 96.4 Leachate,g/l: Pb 163.500 176.700 180.300 [H.sub.2]Si[F.sub.6] 62.900 55.400 52.300 Zn 0.540 0.619 0.683 Fe 0.369 0.415 0.091 Cu 0.050 0.091 0.109 Co 0.006 0.007 0.007 TABLE 4. EFFECT OF [H.sub.2]SI[F.sub.6] CONCETRATION [H.sub.2]Si[F.sub.6]-technical-grade acid 175 g/l 200 g/l 250 g/l 300 g/l Pb% 89.0 97.5 95.4 95.7 Leachate,g/l: Pb 180 179 184 177 [H.sub.2]Si[F.sub.6] 32 56 94 133 Zn 0.57 0.75 0.82 1.00 Fe 0.53 0.61 0.61 0.67 Cu 0.12 0.13 0.13 0.18 Co 0.00 0.00 0.00 0.00 TABLE 5. CHEMISTRY COMPOSITION OF THE SYNTHETIC MIXTURES Compounds Synthetic mixtures (%) I II III Pb 50.000 60.000 PbS 57.740 70.000 80.830 ZnS 5.000 5.000 5.000 CuS 1.000 1.000 1.000 0.050 0.050 0.050 [Fe.sub.2][O.sub.3] 1.010 1.050 1.020 Si[O.sub.2] 29.200 16.900 6.100 [M.sub.2][O.sub.3] 2.000 2.000 2.000 CaO 2.000 2.000 2.000 MgO 2.000 2.000 2.000 Total 100.000 100.000 100.000 TABLE 6. EFFECT OF VARIOUS AMOUNTS OF OXIDANTS Test [H.sub.2] Pb[O.sub.2], Pb, (Pb- [O.sub.2]- gr % 70%) 35%, ml 1 0.0 15.0 90.0 2 2.5 15.0 95.0 3 5.0 9.5 95.0 4 7.5 8.0 96.5 5 10.0 5.0 95.0 6 19.0 0 96.0 TABLE 7. 35% [H.sub.2][O.sub.2] (7.5 ML); PB[O.sub.2] (8 GR) [H.sub.2]Si[F.sub.6] 175 200 250 300 gr/l gr/l gr/l gr/l Pb(%) 85.0 97.5 95.0 95.5 Analysis of leachate, gr/l Pb 180 175 185 175 [H.sub.2]Si[F.sub.6] 30 55 90 130 Zn 0.55 0.75 0.80 1.00 Fe 0.50 0.60 0.60 0.65 Ni 0.10 0.10 0.10 0.2 Cu 0.015 0.02 0.02 0.02 TABLE 8. 35% [H.sub.2][O.sub.2] (7.5 Ml); PB[O.sub.2] (8 GR); [H.sub.2]S1[F.sub.6] (200 GR/L) Pb% ToC t(min) Pb% 50% 70 30 52.5 60 56.5 90 65.3 80 30 54.2 60 58.5 90 67.0 30 56.5 0 60 59.1 90 70.0 60% 70 30 55.6 60 60.2 90 68.7 80 30 57.2 60 63.3 90 71.5 90 30 57.0 60 61.0 90 73.5 70% 70 30 60.5 60 63.8 90 75.0 80 30 65.0 60 72.0 90 79.0 90 30 87.6 60 95.3 90 97.6
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|Author:||Krstev, Boris; Krstev, Alexandar|
|Publication:||Perspectives of Innovations, Economics and Business|
|Date:||Jan 1, 2011|
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