Printer Friendly

The producing of lead and elemental sulfur by new technologies from galenite ores.

Introduction

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][??]

[??]3PbSi[F.sub.6]+4 [H.sub.2]0+2[S.sup.o](1)

[PbSiF.sub.6]+2[H.sup.+]+2e[??]Pb+[H.sub.2]Si[F.sub.6] (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.

General

The chemical equations for PbS leaching in acid solution with and without oxidants are following:

PbS+2[H.sup.+]+[0][??][Pb.sup.2+]+[S.sup.o]+[H.sub.2]0 (3)

PbS+8[H.sup.+]+8[0][??]PbS[0.sub.4]+4[H.sub.2]0 (4)

PbS+2[H.sup.+][??][Pb.sup.2+]+[H.sub.2]S (5)

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)

Pb0+[H.sub.2[Si[F.sub.6][??]PbSi[F.sub.6]+[H.sub.2]0 (8)

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.

previous investigations

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].

Experimental tests

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.

Conclusions

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.

References

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.

BORIS KRSTEV

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
COPYRIGHT 2011 Prague Development Center
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2011 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Author:Krstev, Boris; Krstev, Alexandar
Publication:Perspectives of Innovations, Economics and Business
Date:Jan 1, 2011
Words:2216
Previous Article:Forecasting by econometric models as support to management.
Next Article:Some hazardous appearances in flotation tailings dumps in domestic mines.
Topics:

Terms of use | Privacy policy | Copyright © 2021 Farlex, Inc. | Feedback | For webmasters