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By T. van Sandwijk, G. Van Weert, E. Molleman

This paper reports on test work that explored the dissolution/precipitation reaction: ZnS + 2HCl - ZnC12 + H2S, which is part of a process used in the production of pure ZnS. The research focused on the influence of proton activity on the dissolution of zinc concentrates obtained from the Brunswick Mine No. 12 in Canada (Brunswick Mining & Smelting); the Red Dog deposit in Alaska (Cominco Ltd.); and the Tara deposit in Ireland (Outukumpu Zinc). A comparison between the results of the experimental dissolution as a function of pH and the dissolution predicted by thermodynamics suggest that the three concentrates contained sig¬nificant amounts of the more reactive mineral wurtzite, although XRD analysis showed mainly the presence of the mineral sphalerite.

Jan 1, 1999

By S. A. Braley

THE first commercial production of bituminous coal in the United States was in 1820, and formation of acid in the areas from which the coal was removed began at that time. Thus it is 130 years since the development of mine acid began. The coal operator has had to deal with the acid water produced in his mines, and his losses from corrosion of pumps and equipment have been tremendous. Other industries and the public have been forced to spend large amounts for their water requirements because of the acid discharge from the mines. There are many contradictions in the literature on this subject probably because of variations in the analytical procedures followed and differences in the methods of calculation and reporting. The opinions previously expressed may be summarized as follows:

Jan 8, 1951

The New South Wales Department of Mineral Resources has, since 1974, administered the Derelict Mines Rehabilitation Program (DMRP) to reduce the environmental impacts of abandoned and orphan mine sites. The application of the DMRP is presented in case studies of sites from the South Maitland Coalfield featuring residual drainage of acidic and saline water in a semi urban and rural community setting. The acidity here is typically derived from iron oxidation in shallow underground coal mine workings and in surface emplacements of coal washery reject materials. This paper presents summary information on AMD investigation, monitoring and rehabilitation. The experiences of community expectation, stakeholder consultation and peer review are discussed.

Jan 1, 2003

By Charles A. Sorrell

Two red muds, two fly ashes, and several aluminosilicate minerals were subjected to direct treatment with concentrated H2SO4 at temperatures of 175°C and below. X-ray analysis showed that virtually all the sulfate reaction products remained in the solid residue because of their low solubilities in x SO Substantial portions of the Al2O3 Fe2O3TiO2, Na2O, and K2O components of the materials reacted to form water soluble sulfates, which were then removed by H2O leaching at 55°C. The solid residue after water leaching consisted largely of amorphous silica and, in lime bearing compounds, CaSO4, The reaction and leaching processes were effective in removing all or nearly all the Al2O3. Fe2O3, TiO2, Na2O, and in lime components in the fly ashes, red muds, china clay, bentonites, the nephelioe fraction of nepheline syenite, and a plaster insulating brick composed of anorthite and mullite. Reaction with potassium feldspar and petalite took place, with formation of alkali aluminum sulfates, but the reaction rates and yields were extremely low. Potassium feldspar can be heated with Na2O and x O in air at 700°C for 24 hours, or with CaO at 1000°C for 24 hours, after which the reaction product kaliophilite, nepheline, and leucite-like phases, prove to be very susceptible to H2SO4, reaction and H2O leaching, providing yields near 100% of the Al2O2 content. An alternative method of H SO treatment consists of heating the sample in a silica tube and passing H2SO4 vapor over it. Preliminary results indicate that this method can be effective in enhancing the kinetics of reaction with the Al O component of potassium feldspar and offer the possibility that formation of Al2 (SO ) Fe2(SO4)3 and TiOSO4 can be accomplished selectively by taking advantage of the fact that the upper stability limits of the respective sulfates in the presence of H2SO4 vapor will be different.

Jan 1, 1982

By L. W. Beckstead

The use of acid ferric sulfate solution as a lixiviant for chalcopyrite concentrates has been of little interest from a practical standpoint due to the formation of a tenacious layer of elemental sulfur which severely impedes the reaction progress. CuFeS2 + 4Fe+3 ?Cu+2 + 5Fe+2 +2s° For example, an acid ferric sulfate leach of chalcopyrite concentrate results in only 12% copper extraction in a three hour leach at 93°C. Experimental results suggest that particle size is the only controllable variable which has a significant effect on the rate of acid ferric sulfate leaching at ambient pressure. Size reduction of the concentrate prior to leaching was exam¬ined using various methods of grinding. Of the grinding methods considered, attrition grinding was found to be the most effective. Leaching of an attritor-ground product (median particle size 0.5 microns) resulted in approximately 90% copper extraction in a three hour leach at 93°C. Energy measurements suggest that the costs associated with attrition mill¬ing are not unreasonable. Evidence indicates that "activation" or stored strain energy is not responsibile for the enhanced reaction kinetics of the finely ground concentrate, but rather the experimental results can be explained simply in terms of the increased surface area due to size reduction. Leaching reaction mech¬anisms operative in the acid ferric sulfate system are discussed and the application of ultra-fine grinding technology to other systems is considered.

Jan 1, 1976

By A H. Clemens, P Lindsay

Acid producing potential static tests have been undertaken on sample lithologies from New Zealand coal mines, to rank the lithogies into acid producing waste rock and stable non-acid producing waste rock. Results indicated that the main acid producing waste rock in the Waikato coal region are the marine Whaingaroa siltstone and the Glen Massey formations and the main alkaline producing lithologies were the Tauranga group volcanic-derived sediments (A & D) and the Mesozoic basement. Coal ash analysis of 28 samples from 28 mines have also been analysed for reactive S percentage and their base potential has been quantified by the chemical index of alteration (CIA). The results provide mine management in the Waikato Coal region with a classification of problematic and stable waste rock types. XRF and CIA values determined from wash drill cuttings would provide a method of determining waste rock volumes and magnitude of palaeo-weathering underground.

Jan 1, 1999

By A R. Gerson

Pyrite, chalcopyrite and mixed sulfide samples, with and without quartz (5 wt per cent S), were subjected to column leaching to mimic natural weathering (cyclic wetting and drying). The pH and SO4 2- concentration of the column effluent was measured over a period of 78 weeks. The pH of the pyrite-only containing column rapidly decreased and remained under pH 4 after 12 weeks of leaching. The pH calculated assuming a 2:1 ratio of H + generation and SO4 2- release was slightly lower than that measured. However, a reduced H + to SO4 2- ratio of 1:1 is predicted if the release of aqueous Fe 2+ is assumed rather than the formation of Fe(OH)3. The pH of all columns containing only chalcopyrite or a 1:1 mole ratio of chalcopyrite and pyrite remained at or above pH 5 for the duration of the leach even though significant SO4 2- was released. One column containing the same initial surface area of pyrite and chalcopyrite but only approximately 0.10 the mole fraction of S as chalcopyrite maintained a pH of greater than five for the first 56 weeks of leaching and showed sporadic acid production thereafter. It is well established that oxidation of chalcopyrite results in a surface layer of polysulfide material. It is the formation of polysulfide that neutralises the acid produced on S oxidation through to SO4 2-. Hence where polysulfide formation occurs extensively on chalcopyrite the resulting solution pH decrease will be less than that based on SO4 2- production. The oxidation rate of sulfide minerals increases with decreasing pH and hence acid formation via sulfide oxidation to SO4 2- causes the subsequent oxidation rate to increase. The addition of calcite (CaCO3)to a pyrite column not only neutralises the acid formed but also decreases the rate of release of sulfate to solution by a factor of approximately 30. This is also the case where chalcopyrite is present mixed with pyrite. The rate of release of sulfate from the mixed sulfide mineral columns (after the initial release of the sulfate already present) was between one-fifth and one-tenth that in the absence of chalcopyrite.

Jan 1, 2003

By P. G. West-Sells

At Barrick's Zaldivar Copper Mine in Chile, the addition of sulfuric acid to the ore going to heap leaching is a major expense. A process in which a portion of this acid is replaced by elemental sulfur added to the heap has been developed by Barrick and Westcoast Biotech that has the potential for significant cost savings. Initial shake flask tests with plant raffinate solution indicated that oxidation of elemental sulfur by a culture of sulfur-oxidizing bacteria, some indigenous to the Zaldivar heap, showed a significant lag period. This lag period could be reduced by dilution of the raffinate, but dilution would not be economical to implement at Zaldivar. Short (0.75 m) column tests indicated that after the initial lag period, sulfur biooxidation occurred steadily and the acid requirement for obtaining the same copper recovery as the control without sulfur was reduced by as much as 13 kg/t. These tests were followed by taller (5.1 m) column tests that confirmed the reduction in acid consumption, with no negative effect on copper extraction.

Jan 1, 2007

By Jeffrey Anderson, Cindi Byrns, Andy Davis

A closure plan was developed for the Intera Pond Facility, a former acid leaching collection pond at the BHP Robinson Mining Operations. To properly close the Intera Pond Facility, an engineering plan that was both technical and cost effective was developed. A primary objective of this closure project was to demonstrate to State regulators that following the proposed plan would minimize further degradation of water resources. Field data demonstrated natural attenuation of metal enriched solutes via carbonate reactions. Prospective fate and transport modeling indicated that it would not continue to degrade waters of the State.

Jan 1, 2000

SULFURIC ACID U.S. 4,070,260 - Sulfuric acid leaching of willemite, hemimorphite, or other zinc silicate ore. Ore is leached with at least a stoichiometric amount of a IN to 6N sulfuric acid solution at a temperature near its boiling point to form a gelatinous mass of hydrated silica and zinc sulfate, the water in the mass partially evaporated to crystallize all of the silica, the mass treated with hot water to dissolve substantially all of the zinc sulfate, the suspension filtered, and zinc values recovered from the filtrate by electrolysis. N. Dreulle, assigned to Compagnie Royale Asturienne des Mines. Jan. 24, 1978. 3 pp. (204-119). Filed: 2-10-76 (656,966) . Priority: France, 2-14-75 (75/04594) .

Jan 1, 1979

US 4,132,758-Leaching of copper sulfide ore using nitrogen dioxide as the oxidant A slurry of ore in sulfuric acid is contacted with a nitrogen dioxide-containing gas at a temperature below 11 5" C and a pressure of from atmospheric to 35 PSI, the slurry agitated, and the resulting nitric oxide from the slurry regenerated to nitrogen dioxide for reuse About 90% of the copper In the ore IS dissolved, and the leach solution is separated for further processing. This procedure is also useful for sulfide ores of silver, molybdenum, nickel, cobalt, and zinc T C Franklewicz and R E Lueders, assigned to Kennecott Copper Corp Jan 2, 1979 7 pp (423-27) Filed 1 1-30-77 (855,983) (Drawings below ) US 4,138,231-Wet-cleanlng of gases from the roasting of copper sulfide ore, zinc sulfide ore, pyrite, or arsenopyrite The gases are washed in dilute sulfuric acid circulating in a closed system, the wash water treated to remove arsenic, the washed gas condensed by cooling; and the condensate separated, purified of residual arsenic, and neutralized B G V Hedenas, J E Wiklund, T R H Johansson, and KA Melkersson, assigned to Boliden AB Feb 6, 1979 7 pp (55-71). Filed 3-30-77 (782,908) Priority Sweden, 4-9-76 (76/04,219) (Flow diagram at right ) US 4,148,862-In the acid-leaching of silicate-bearing calcined zinc sulfide ore, finely divided calcine is leached at elevated temperature with sulfuric acid, and additional calcine is added at an optimum rate to precipitate SI~ICIC acid in the same stage In an easily settling, readily filterable form Reactions take place at a silica concentration so low that the solution is not greatly oversaturated An anionic flocculant- may be added to the slurry immediately before the filtration step S. P Fugleberg and J T. I Poijarvi, assigned to Outokumpu Oy Apr. 10, 1979 4 pp (423-106). Filed 10-6-77 (840,041) Priority Finland, 10-8-76 (76/2880)

Jan 1, 1980

US 4,192,851-Recovery of elemental sulfur and the metal values from a complex sulfide ore containing two or more of the metals zinc, lead, copper, silver, gold and/or other metals. A mixture of ore and sulfuric acid and/or spent electrolyte is flowed at optimum temperature and pressure in a quiescent zone to dissolve selected metals and sulfur and coalesce the sulfur. The coalesced sulfur and unreacted sulfides are separated by flowing the leach slurry with an upward velocity component The separated materials are discharged and further processed by conventional methods as war- ranted. H.E. Hirsch, J F. Higginson, EG. Parker, and G M Swinkels, assigned to Sherritt Gordon Mines Ltd. Mar. 11, 1980. 6 pp. (423-28) Filed. 3-14-78 (886,368). Priority. United Kingdom, 3-15-77 (10800/77).

Jan 1, 1982

By S. Vukcocic

A long term research project is in progress to establish the parameters of an acid leach process to recover alumina 'froui' high-iron and/or low-iron white bauxites, kaolinite, coal. ash and copper mine tailing. In this paper the results of acid leaching of copper flotation tailing for the removal of alumina are presented. The tailing is very complex material which contains 25% Al203 in the -10 lim fraction. X-ray diffraction indicates presence of quartz, kaolinite and minor 'alunite. After classification and ,separation of the -10 lim fraction, the raw material is fired to 550GC and leached at 90GC. Filtration is applied for the separation of white silicate residue form leach liquid. After the purification step, aluminum salt is crystallized from the solution, and calcined to alumina. Kinetic correlation and regime, of the processes are defined and presented in the paper.

Jan 1, 1992

Mineralogical analysis of a nickeliferous laterite from the Rockhampton region shows that the nickel is largely associated with the manganese wad and opaline silica. The laterite also contains an appreciable chromite content (about 12 per cent Cr2O,) although this tends to be poorly liberated.Leaching with hydrochloric or sulphuric acid, at atmospheric pressure at the boiling point is non-selective with respect to iron dissolution.The degree of dissolution increases as the acid concentration and retention time are increased; cobalt dissolution requires less aggressive conditions than does the dissolution of an equivalent amount of nickel.Leaching with sulphuric acid at elevated temperatures and pressures leads to a minimum amount of iron dissolution, is rapid, and requires a reduced acid addition rate. Nickel and cobalt recovery from the clarified leachate would be simplified because of the leach selectivity.Pressure leaching appears to be the most practical route for treating the Rockhampton laterite. The economics of processing would be made more attractive by the recovery of a chromium concentrate from the leach residue. This would typically contain about 45 per cent Cr2O, and could be used as a source of chromium chemicals.

Jan 1, 1986

By T. Sharma, T. C. Rao

Laboratory studies have been carried out on acid leaching as a possible route for the extraction of potassium from glauconitic sandstone. Leaching efficiencies with sulphuric, hydrochloric and nitric acids were investigated. The effects on potassium dissolution of temperature, concentration and type of acid, stirring speed and leaching time were also studied. The results show that it is possible to recover 87.5, 93 and 85% potassium with 5 M H2SO4, HCl and HNO3, respectively. During the initial stages of the sulphuric acid leaching process the chemical reaction at the mineral surface is the rate determining step, whereas during the later stages diffusion through the product layer is rate-controlling. Overall, the process follows a mixed-control model that includes both chemical reaction and diffusion. The activation energy for the dissolution of K was found to be in the range 25.79-106 kJ/mol.

Jan 12, 1992

By F. Enslin

Heavy metals and sulphates in acid mine drainage (AMD) can beadsorbed onto bentonite clay, leaving clean water and a heavy metal loaded clay precipitate as products. Due to the toxicity of heavy metals, the clay could not be disposed of safely in the past. A method was thus required to remove the heavy metal content from the clay. Acid leaching was proposed to liberate the heavy metals from the loaded clay. Sulphuric, nitric and hydrochloric acid were considered as lixiviants. Loaded clay samples were leached over a range of pH values from 1 to 3.5 to identify an optimum leaching condition. From the results it was found that metals can berecovered from loaded bentonite clay by means of acid leaching and the optimum pH for heavy metal liberation was found to be 2.5, with uranium as an exception, being optimally leached at a pH of 3. This allows for the possibility of selective leaching. Furthermore, X-ray diffraction analyses indicated that the clay structure did not deteriorate significantly during acid leaching, suggesting that the bentonite could be reused. The treatment of AMD with bentonite clay, and subsequent acid leaching of the clay, is a sustainable solution, and current outcomes could possibly lead to industrial implementation of the process during water purifying and metal recovery from waste streams. Keywords: Acid mine drainage, bentonite, heavy metals.

Jan 1, 2010

By Shiou-Chuan Sun

This paper is to be presented at the Annual Meeting of the American Institute of Mining, Metallurgical and Petroleum Engineers, New York, New York, February 18-22, 1962. Permission is hereby given to publish with appropriate acknowledgments, excerpts or summaries not to exceed one-fourth of the entire text of the paper. Permission to print in more extended form subsequent to publication by the Institute must be obtained from the Secretary of the Institute. If and when this paper is published by the Institute, it may embody certain changes made by agreement between the Technical Publications Committee and the author, so that the form in which it appears here is not necessarily that in which it may be published later.

Jan 1, 1962

By Chang Wei, Fan Zhang, Zhigan Deng, Minting Li, Cunxiong Li, Gang Fan, Xingbin Li

Marmatite is an important resource of zinc, which exist in forms of high iron and high indium. In order to recycle the valuable metal from these ores, the testwork of simultaneous leaching on neutral residue mixed with zinc concentrate of high iron and high indium has been conducted. The primary objectives are to leach the zinc and indium remaining in the neutral leach residue as ferrite using acid, and to reduce the ferric iron in solution to the ferrous by zinc concentrate, thereby extracting the zinc and indium in the zinc concentrate. The results indicated that in the following conditions, mass ratio of neutral residue to zinc concentrate of 1:0.25, particle size of 74-58 μm, initial sulfuric acid concentration of 150 g/L, liquid to solid ratio of 8 L/kg, temperature of 90°C, reaction time of 4h, the leaching efficiency of zinc and indium were over 95%, nearly 90% Fe was Ferrous in the leaching solution. This process effectively extracted zinc and indium and converted Fe3+ into Fe2+ in solution, and simplified the traditional process of reduction after leaching.

Jan 1, 2016

By Ronald D. Hill, Elmore C. Grim

The removal of overburden often exposes pyritic materials (iron disulfide). As shown in equations 1 and 2, the oxidation of this material results in the production of ferrous iron and sulfuric acid. The reaction then proceeds to form ferric hydroxide and more acid, as shown in equations 2 and 4. [ ] Consequently a low pH water is produced (pH 2-4.5). At these pH levels, the heavy metals such as iron, manganese, copper, and zinc are more soluble and enter into the solution to further pollute the water. Water of this type supports only limited water flora, such as acid-tolerant molds and algae; it will not support fish life, destroys and corrodes metal piers, culverts, barges, etc., increases the cost of water treatment for power plants and municipal water supplies, and leaves the water unacceptable for recreational uses. The amount, and rate of acid formation, and the quality of water discharged are a function of the amount and type of pyrite in the overburden and coal, time of exposure, characteristics of the overburden, and amount of available water(l). Crystalline forms of pyritic material are less subject to weathering and oxidation than amorphic forms. Since oxidation by oxygen is the primary reaction during early acid formation, the less time pyritic material is exposed to air, the less acid is formed. Thus, a positive preventative method is to cover pyritic materials as soon as possible with earth, which serves as an oxygen barrier. In terms of mining, this step is accomplished by current reclamation techniques and small open pits.

Jan 1, 1974

By David J. Akers

In past years, water drainage control in coal mines has been primarily directed on the basis of water quantity rather than quality. Due to the recent intense interest in total ecology and environment, emphasis has shifted to the point where the water exiting from a mining operation may be of better quality than when it enters. In most operations this has meant the use of treatment methods (neutralization) while the technology for the prevention of acid drainage is being developed or refined. To date, underground abatement of acid formation has generally been less expensive but also less effective than surface treatment of the mine water. It seems probable that total mine water pollution control will have to include both underground abatement and surface treatment methods. The general acid producing reaction involving the oxidation of pyrite - 2FeS2 (pyrite) + 702 + 2H20 ? 2Fe2S04 + 2H2SO4 - is well known, even though the individual steps are not clearly understood. The major implication of this reaction, that acid production can be eliminated by not allowing the contact of pyrite with free oxygen or water, has been well substantiated both in the laboratory (1,2) and in practice. (3) Underground abatement or control processes can be generally classified into two types: (1) the effective control or elimination of acid causing reactions within the mine, and/or (2) the reduction or prevention of water flow into and out of the mine. Recognizing the fact that these two types may be directly inter-related, this paper will, for the purposes of clarity and simplification, discuss each separately.

Jan 1, 1973