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By R J. Tremblay, R. R. Hoffman

This paper deals with materials of construction and problems encountered and overcome in leaching and filtration of oxidized sulphuric acid slurry in the Port Radium mill after eight years of operation. The slurry is characterized by a high calcium sulphate content as well as a high chloride level under oxidized conditions, both of which affected initial design and subsequent changes. Leach agitation tanks are of wood with a mild steel superstructure and stainless steel agitator and moving parts below solution level. Electro-polished 316 stainless steel cooling coils are used for temperature control of the slurry. The string filters are of the Oliver type with wood decking. Extensive use is made of wood, Linatex lined mild steel and stainless steel for the slurry handling. A typical analysis of the slurry solution follows:(pH-1.30) ClOa Fe+++ Free Acid UaOs c1-so.--0.10 gms/litre 10.2 gms/litre 6. 7 gms/litre 3.5 gms/litre 2.0 gms/litre 155 gms/litre

Jan 1, 1961

By Michael Sheedy

Sulfuric acid is widely used as an electrolyte for the electrorefming and electrowinning or metals. Impurities in this electrolyte are controlled by continuously bleeding solution from the tank house. In addition to the contaminant these bleed streams contain high levels of sulfuric acid and the metal being recovered. Subsequent treatment of these bleed streams often requires neutralization which generates large volumes of solid waste. Absorption resin technology employing a novel ion exchange technique known as Recoflo® allows the separation of the mineral acid from dissolved metal salts. The recovered acid is suitable for recycle back to the electrolyte circuit. The metal salt and other contaminants leave the process free .of the sulfuric acid. In this process, known commercially as the APU®, ion exchange resin is used to sorb sulfuric acid while excluding the metal salts. The purified acid is then removed by washing the resin with water. The process has been extensively used for the recovery of waste pickling acids in the steel industry and anodizing solutions in the aluminum industry. In the mining and metallurgical industries the process has been successfully evaluated for the separation of excess sulfuric acid from copper electrolytes, the removal of magnesium and manganese contaminants from zinc electrolytes, and nickel and copper from copper electrolytes. A full scale installation on a copper refinery bleed stream at Palconbridge's Kidd Creek plant in Timmins, Ontario has now been operating successfully for more than 1 year while pilot field trials have been successfully completed on other applications.

Jan 1, 1997

By Richard S. Dennis

Acid recovery employs ion exchange (I-X) resin as separation media for inorganic acids from dissolved metallic salts by physical adsorption and without the use of chemicals. This technology has been used for years on spent etching and plating liquors to recover acid for reuse in the bath and to reduce waste acid neutralization costs. It is also used for electrolyte treatment to facilitate valuable metal recovery via acidity reduction. TETRA's ccrxr'" I-X contactor has been used successfully for acid separation from its metallic salt counterpart in a simple, continuous operating mode using strong base anion resins. Efficient separation is enhanced by acid reconcentration to nearly its original strength or as high as 14-20%. Continuous treatment also recovers heat to the tankhouse or bath and improves metal quality due to consistent acid quality. Conventional fixed bed ion exchange (I-X) systems are impractical for acid recovery because of complex control design and large resin inventories needed to process very low liquid-to-resin treatment ratios associated with strong acid concentrations.

Jan 1, 1996

By F. Baerhold, S. Mitterecker

"Acid recovery is an important process step in pickling and leaching processes. Pyrohydrolysis in spray roasters and fluidized beds is a well-established technology to recover hydrochloric acid, but the hydrolysis in the liquid phase is more and more considered as an alternative new process route. The characteristic features of these three processes will be discussed along with select industry trends. For example, hydrochloric acid based leaching processes for ilmenite and nickel laterite ores produce far larger volumes of waste acid streams than the steel industry. Scaling-up of the spray roasting technology to the highest possible capacity is necessary in order to become more cost effective. In addition, process routes based on ferric chloride pyrohydrolysis allow the production of super-azeotropic HCl (up to 30 wt.%). Finally, the new ECOmode concept optimizes the operation of both pickling lines and the spray roast acid recovery plant. Long term results from industrial applications show that fuel savings in the spray roaster of 25% are easily achieved without additional process steps. An attractive feature is also to upgrade existing installations to higher plant capacities.INTRODUCTION Pyrohydrolysis is the conversion of metal halides into metal oxides at elevated temperatures in the presence of water vapor. Reaction products are a hydrogen halide gas and a metal oxide. The process was originally developed and introduced into the market by ANDRITZ Ruthner in the 1960’s. It has found wide technical application in the field of acid recovery and oxide production. The introduction of this process has revolutionized pickling technology. The use of hydrochloric acid has strongly increased over the last decades, since pyrohydrolysis is available for the total recovery of waste pickle liquors from mild steel pickling, as illustrated in Figure 1.Chloride media are also used increasingly in the metallurgical industry. Oxide production processes for Mg, Co, Ni, and Al have been installed. Processes using hydrochloric acid are known for the leaching of ores as well as for the re-extraction of metals from organic solvents. In both cases the recycling of HCl is of substantial importance to achieve highly economic processes and to reduce waste."

Jan 1, 2016

By A. Davis, K. Nelson, C. Webb

Abandoned mines in parts of the Black Hills of South Dakota have the potential for acid rock drainage. For this work, ten sites were examined on Black Hills National Forest land or on private land whose drainage could affect Forest Service land. Water samples from all the sites had pH values less than 6. Results of analyses from water samples and rock samples showed a correlation between metals content and pH. Acid-base accounting was used to determine acid drainage potential of the sites. One site (King of the West Mine) had a high potential for acid generation; fortunately, little or no surface runoff leaves the mine site. Six sites appeared to have moderate potential, including the Minnesota Ridge Mine, which currently is being remediated. Three of the sites had low acid drainage potential.

Jan 1, 2004

By José A. Rios, José A. Vidalôn

The case study of a highland area in the Central Andes of Peru, where many abandoned polymetallic mines are found, is presented. Some of these mines generate metal leaching and acid rock drainage (ML/ARD) or have potentially ARD generating (PAG) tailings/waste rock storage. Effluents are discharged into the first of two lakes in line, which act as reservoirs for irrigating an important valley in the desert coastal region. Drainage fees, their relationship with the deposit and the solid-wastes mineralogy are discussed, as well as variations in water and sediments composition, the benthos, and the aquatic/riparian flora/fauna in these lakes.

Jan 1, 2000

By R Carreau

The results of a detailed acid rock drainage (ARD) prediction program were used to revise the waste rock segregation criteria at the Restigouche open pit mine. Waste rock at the site was predominately derived from altered volcanic rocks that hosted a massive sulfide lead/zinc orebody. The program assessed the five years of drainage chemistry from both the potentially acid generating and the non-acid generating waste rock storage facilities in addition to laboratory-based kinetic test results. Material-specific leaching characteristics including relative metal-release rates and neutralisation potential depletion rates were determined from 12 laboratory-based kinetic tests. Solid-phase analyses indicated that, although pyrite was typically the most abundant sulfide mineral in the waste rock, its abundance varied significantly as documented by total sulfur contents ranging from 4.0 per cent. Kinetic test results were used to establish revised waste rock segregation criteria based on total sulfur content and neutralisation potential. The revised criteria maintain that waste material with a total sulfur content 4.0 per cent as potentially acid generating. When present in sufficient quantities, ankerite provided an effective source of neutralisation potential for the range of observed sulfide oxidation rates. Kinetic testing documented that up to 6 kg CaCO3/t was ineffective at neutralising acidity in samples that contained >4 per cent S. The carbonate molar ratio measured from the humidity cells was adjusted to reflect the stoichiometry of the ankerite and applied as an NP/AP criteria for waste rock containing 0.1 <S per cent <4.0.

Jan 1, 2003

By H Barrie, L Ameglio

"Current methods for acid rock drainage (ARD) mitigation revolve around insulation of the waste from oxygen in the atmosphere with water and dry (soils and liners) covers. Both are of limited effectiveness and present significant drawbacks. Furthermore, while they reduce oxygen influx, they reduce but do not prevent ARD.The inert gas mixture (IGM) technology has been designed to overcome the deficiencies of gas transfer into tailings and waste rock materials across the surface and instead block oxidation by controlling the transfer of oxygen from the atmosphere. Inert gas is injected into the mine waste at low flow rates and the positive but low flow purges the oxygen that tends to diffuse into the sulfide waste across the surface. The positive flow of IGM compensates for inward oxygen diffusion and creates a pressure drop across the cover layer preventing inward diffusion of oxygen and, hence, acid generation.The IGM processes are evaluated in this paper: theoretically, with a review of the theory of ARD and the current state of knowledge about the performance of notably dry covers as atmospheric oxygen barriers via models to predict the performance of the IGM technique practically, with a bench-scaled experiment.The results demonstrate the effectiveness of IGM to prevent oxidation of sulfide minerals and ARD in waste rock. The laboratory experiments further identified key variables to be used to monitor performance and control efficiency of IGM, which is now awaiting field-scale application.The IGM technology is a patented process by Terraquest Technologies Ltd (Canada) in USA, Canada and Australia. The IGM technology can be cost-effectively manufactured on-site with commercially available compressors and gas filtration membranes. It is predicted that low-cost covers can then be utilised with IGM, which in turn lowers the overall capital costs of ARD mitigation.CITATION:Ameglio, L and Barrie, H, 2015. Acid rock drainage prevention using inert gas mixture technology, in Proceedings Tailings and Mine Waste Management for the 21st Century, pp 85–96 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Jul 27, 2015

By G. M. Wilemon

The U.S. Bureau of Mines has conducted preliminary investigations on the leaching of phosphate ores obtained from deposits in the western United States using sulfuric acid (H2SO4) in the presence of methanol. Phosphate extractions in excess of 80 pct were obtained on an ore sample from Pocatello, ID. Initial leaching studies using the ore as received yielded extraction levels of approximately 35 pct. However, when the sample was ground for as little as 5 min in a rod mill, in methanol, then treated with HzS04, 82 pct extraction was achieved. The R2O3-P2O5 (R2O3 = Al2O3 + Fe2O3) ratio of the starting material was 0.11. Solubilized products after leaching exhibited an R2O3-P2O5 ratio of 0.02, which is well within desired limits. These results illustrate the potential of acid-alcohol leaching for recovering phosphate values from marginal-grade ores and as an alternative to methods involving current beneficiation techniques that yield lower phosphate recoveries.

Jan 1, 1992

By M. Gomo, L. S. Mokhahlane

"Underground coal gasification (UCG) is an unconventional mining method that converts coal in situ into a fuel gas that can be used for electricity generation. Residue products from UCG have the potential to leach into surrounding groundwaters. The geochemistry and leaching dynamics of these products are explored in this study. The products include char, ash, and the heat-affected zone in the surrounding rocks. Core samples from the pilot plant at Majuba are the first ever to be recovered from a UCG cavity in Africa, and they give key insights into the geochemistry of the gasification zone. Mineralogical and chemical analyses were performed on the samples, and acid-base accounting (ABA) was used to predict the acid-producing capacity of the gasification zone, particularly for char samples. Some of the char contained pyrite, although not all samples were acid-producing as determined by the ABA analysis. The ABA results showed that some of the unburned coal has moderate levels of sulphur, which could be the driving medium for acidic conditions. The ABA analysis indicated that water in contact with the gasification zone would eventually have a pH lower than 7, which could lead to acid rock drainage. These results form part of a preliminary investigation into the geochemistry of the reaction zone, post gasification. IntroductionUnderground coal gasification (UCG) is an unconventional mining method that converts coal in situ into a fuel gas that can be used for industrial purposes, including electricity generation. The gasification process leads to the formation of a cavity composed of char, rubble, and void space (Bhutto, Bazmi, and Zahedi, 2013). Residue products from UCG have the potential to leach into groundwater. These products include char (devolatilized coal), which can generate acid rock drainage (ARD). ARD is caused by the oxidation of sulphide minerals, which acidifies the leachate, thus increasing the solubility of some environmentally toxic metals (As, Cd, Hg, Pb, Zn, etc.) (Bouzahzah et al., 2015).The main source of ARD is oxidation of sulphide-bearing minerals due to interactions with oxygen, water, and microorganisms (Simate and Ndlovu, 2014; Kefeni, Msagati, and Mamba, 2017; Bouzahzah et al., 2015). Although ARD occurs naturally, it can be enhanced by mining activities that escalate exposure of sulphide minerals to water, air, and bacteria (Simate and Ndlovu, 2014). At the Majuba pilot plant, the unburned coal remaining in the cavity has been in contact with groundwater since the gasifier was shut down in 2013. It is possible that in a commercial UCG plant, most of the coal will be consumed and no unburnt coal will be left in the cavity. Most of the sulphur will be converted to H2S during the gasification process and transported with the syngas to surface, where it can be removed and captured as elemental sulphur."

Oct 1, 2018

By W. W. Rudolph, L. N. Trevani, P. R. Tremaine

UV-visible spectroscopy, Raman spectroscopy, and vibrating tube densimetry have been used in our laboratory to determine equilibrium constants of aqueous species at temperatures as high as 325 °C. The UV-visible and Raman spectra of solutions containing metal complexes and ionized acids or bases can be used to yield formation constants by applying curve fitting methods to resolve the contribution of each species. Colorimetric pH indicators identified by Johnston and coworkers at the University of Texas (Austin) provide an alternative means of determining ionization constants and the pH of complex mixtures. High precision density measurements over the same range yield standard partial molar volumes, which are key parameters for "equations of state" for aqueous species. Examples are given for the copper-ammonia system, simple carboxylic acids, and the iron-sulphate system.

Jan 1, 2004

By H. Bouzahzah

Sulfidic tailings, subjected to atmospheric water and oxygen action, can generate acid mine drainage (AMD); which is the most important environmental problem facing the mining industry. AMD generating potential can be assessed by the static tests which consist of a screening method where the neutralization potential (NP) and the acid-generating potential (AP) of a given rock sample are determined. The AP and NP are determined separately in the different static test existing procedures which can be divided into two distinct classes: chemical and the mineralogical methods. For some chemical method, the AP is calculated on the basis of total sulfide sulfur content in the sample which may overestimate its AP if significant quantities of non-sulfide sulfur species are present (e.g. organic S in coals, some sulfate as gypsum, barite, etc.). However, the mineralogical method evaluates the AP by the sum of the individual sulfides participation on acid generation based on their concentration within the sample and can be more accurate than the chemical method. For AP calculation, the Paktunc (1999a) mineralogical static test takes into consideration all sulfide minerals occurring in the sample. However, it does not take into account the rates of acidity production of these sulfides submitted to weathering conditions. So, the present study focusses on the modification of Paktunc AP calculation by considering the acidity production rates of these minerals. To reach this objective, five base-metal sulfides (pyrite as reference, chalcopyrite, sphalerite, arsenopyrite, galena), diluted within quartz (25?75 wt.%) simulating mill tailings were subjected to a kinetic test to evaluate their AP. The results show that all the studied sulfides minerals generate acidity at different rates, so the Paktunc?s equation for AP calculation has been adapted accordingly.

Aug 1, 2013

By S. H. Ash

NO MORE important question has come before the coal-mining industry in many places, especially in the anthracite region of Pennsylvania, than prevention of stream pollution by mine drainage. Available information on acid mine drainage in the anthracite region of Pennsylvania indicates that a pollution problem must be solved in any program of anthracite mine drainage. The major problem concerns satisfactory disposal of the daily average mine-water discharge of 327,000 gallons per minute (g. p. m.), or 472 million gallons per day (g. p. d.), containing a free-acid load of 431 tons or a total acid load of 934 tons a clay as H2S04. This report indicates the scope of the problem and gives some suggestions concerning its solution.

Jan 1, 1951

By R. J. Pugh

In addition to directly analyzing the surfaces of minerals using high vacuum instrumentation methods, some important surface properties of mineral fillers can be determined indirectly by using reactive chemical probe molecules. This technique enables the strength and the number of the surface reactive sites to evaluation and this type of information is useful in predicting interfacial behaviour of minerals. One method of classifying these surface sites is by using Lewis acid/base theory and this type of approach could enable one to predict the adsorption of functional groups in dispersants, thickeners, pigments, etc. Also the adhesion of polymer matrices to the filler surface may be improved.

Jan 1, 1992

Transport Canada (Federal Government) constructed the Halifax International Airport (HIA) near Halifax, Nova Scotia, Canada in the late-1950s. Site location criteria were primarily; direct access to the city and a raised flat topography. Unfortunately, the site chosen was located on shallow Meguma group pyritic slate bedrock. In 1982, during the construction of an airport taxiway, it became very apparent that acidic run-off from excavated bedrock at the site was having a negative impact on adjacent aquatic habitat. The ensuing 20 years involved many efforts to rectify the acidic drainage problem with mixed results. Some of the techniques which have been implemented at HIA to address the acid rock drainage (ARD) issue include: dry covers, wet covers, wetlands, electrochemical treatment, open limestone channels, limestone gravel polishing beds, agricultural limestone application, and two hydrated lime [Ca(OH)2] addition treatment plants, the first producing low density sludge and the new one that creates high-density sludge. Based on over 20 years of water quality monitoring data it is apparent that only certain acid drainage mitigation methods have been effective at HIA. In 2000 when the Halifax International Airport Authority (the Authority) took control of the operation and management of the airport, including the ARD issue, it was decided to construct a modern, highdensity sludge, hydrated lime treatment system. This new $CAN 7 million system is now in operation and is achieving compliance with water quality guidelines. Due to high operating cost, a review of methods to optimise the system is being carried out. The HIA ARD problem, though minor by comparison to most mine sites, has provided unique challenges and may provide valuable insights into this urgent environmental and financial issue.

Jan 1, 2003

By J Millard, K Sexsmith

BHP Billiton Diamonds Inc (BHPB) has been mining kimberlite from several pipes at the Ekati Diamond MineTM located 300 km north of Yellowknife since 1997. Processing of kimberlite produces coarse kimberlite rejects (CKR, 0.5 to 8 mm) and fine tailings (less than 0.5 mm). The CKR are trucked to the Coarse Kimberlite Reject Storage Area (CKRSA) located within the drainage area of the tailings impoundment (Long Lake Containment Facility û LLCF). The coarse rejects are wet when dumped and are expected to freeze as a result of annual average site temperatures of about -10¦C. Seasonal thawing occurs along the exposed edges of the pile. Monitoring of the CKR indicates they have consistently low sulfur concentrations (0.4 per cent) accompanied by high acid neutralisation potentials (78 to 337 kg CaCO3/t). Carbonate concentrations vary from 0.9 per cent to 3.4 per cent. The CKR are therefore not potentially acid generating based on conventional laboratory testing. Monitoring of stagnant pools on the tundra downgradient of the CKRSA has shown that water originating from the pile resembles acid rock drainage (ARD). Water pHs can be less than 4, and sulfate concentrations are typically in the thousands of milligrams per litre. Conventional flowing toe seeps are pH neutral but also have elevated sulfate concentrations. Investigations conducted in the summer of 2002 revealed no evidence of in situ acid generation. Pore water chemistry is probably controlled by oxidation of fine-grained pyrite, neutralisation of acidity by calcium and magnesium carbonates and silicates, and freeze concentration of pore water. The acidity observed in tundra pools downgradient of the CKRSA appears to be a result of leaching and mobilisation of iron under reducing conditions at the CKR-soil contact. Downstream of the CKRSA, reduced iron oxidises and is hydrolysed on contact with the atmosphere causing pH depression. BHPB is applying the findings of this study by constructing facilities containing kimberlite on granite pads. These in turn are placed on frozen ground so that the foundations remain frozen and limits contact of wastes with the acidic soils.

Jan 1, 2003

By C. C. Walden, A. Bruynesteyn

"Chemical and biological aspects of the formation of acidic effluents from sulfide waste materials are discussed. Test procedures to determine the acid producing potential of waste materials, as well as the characteristics of such acidic effluents, are presented. Practical applications of the test procedures are discussed with reference to predictior of environmentally unacceptable drainage and to estimation of metal recovery by dump leaching.INTRODUCTIONNatural leaching of sulfide minerals, exposed to the atmosphere, has been occurring for geological time. For centuries, man has been aware of the acid drainage originating from coal workings, copper mines and waste dumps. With the advent of the technical sciences, the processes involved in acid mine drainage production were considered to be solely chemical in nature. However, in 1947, it was shown (1) that a specific microorganism, called Thiobacillus ferrooxidans, was responsible for acid mine drainage from coal workings. It was demonstrated that under suitable conditions - this bacterium oxidized pyrite and marcosite in the coal to ferric sulfate and sulfuric acid. Numerous studies have subsequently demonstrated that - under suitable conditions - Thiobacillus ferrooxidans can attack most sulfide minerals, producing weak sulfuric acid, oxidizing ferrous to ferric iron and solubilizing other metals present (notably copper and zinc) as their sulfate salts."

Jan 1, 1980

By G. P. O’Malley, A. N. Nikoloski

One of the most promising options for extraction of copper from low-grade chalcopyrite ores by heap leaching, however, chalcopyrite is refractory and suffers slow leaching kinetics and poor overall extraction due to formation of a passivation layer on the particles. The solution composition is believed to strongly affect the formation of this layer. This paper examines the effects of the major cationic species of Fe3+/2+, Mg2+, Cu2+, and Al3+ and the anionic SO42− species in acidic ferric sulfate media with a composition simulating recycle heap leach conditions. It was found that altering the sulfate, iron or aluminium concentration had significant effect on the copper extraction, the concentration of copper slightly influenced the extraction, and the amount of magnesium had no appreciable effect. Also, iron and aluminium caused a change in the sulfate concentration, and the sulfate ions had the greatest influence on the extraction of copper under recycle leach conditions

Jan 1, 2023

By G. Demi, G. Belardi, N. Shehu, S. Cico

The physico-chemical interaction between minerals such as olivine, chromite and serpentine and the ions most commonly present in solution, like Ca and Mg and flotation reagents such as EDTA and oleic acid was investigated. The study was conducted via release tests, electrophoretic measurements and microflotation of selected minerals coming from the Kukes deposit (Albania).

Jan 1, 2003

By G. Demi, G. Belardi, N. Shehu, S. Cico

The physico-chemical interaction between minerals such as olivine, chromite and serpentine and the ions most commonly present in solution, like Ca and Mg and flotation reagents such as EDTA and oleic acid was investigated. The study was conducted via release tests, electrophoretic measurements and microflotation of selected minerals coming from the Kukes deposit (Albania). The results were confirmed by means of beneficiation tests on various types of ores, from the Kukes (Kalimash), from Bulquiza area and from the Rizo deposit (Greece). It has been demonstrated that when Na-K Oleate is used as collector chromite, olivine and serpentine can be separated at pH = 2.5 and/or 5.5 employing EDTA (EthyleneDiamineTetraAcetate) on previously deslimed material. This approach ensures flotation concentrates with a Cr2O3 content about 50%, at a recovery in excess of 65%.

Jan 1, 2003