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By G H. Reavely, The University of Western Ontario Department of Geology

The lower Middle Devonian Sylvania Sandstone occurs in the sub-surface in the western part of Mal-den township, Essex county, Ontario. The formation is composed of well rounded, frosted quartz grains with a silica content varying from 42 to 93 per cent and the grains are cemented by carbonate, constituting up to 57 per cent of the rock. This sand-stone is not a homogeneous bed but is divided by strata rich in carbon-ate cement. The thickness of the Sylvania in Malden township varies up to a known maximum thickness of 88 feet. The lower contact with the chert-bearing Bois Blanc formation is sharp but the upper contact with the Amherstburg formation (Detroit River group) exists as a transition by a gradual downward increase in quartz grains. The Sylvania would seem to outcrop in the lake bottom near the mouth of the Detroit River dipping to the north along a broad anticline the axis of which follows the Detroit River. Just south of Amherstburg, a local east-west trending

Jan 1, 1961

By J. G. Stevens, S. W. Colley

"Selective separations of metals and ions in mineral extraction and refining are becoming more challenging as ore bodies become more complex and environmental pressures increase. The separation and containment of mercury produced in gold mining are a factor in the profitability and operability of mines. This paper will discuss the development and implementation of the Johnson Matthey HgFree selective mercury removal process. The process is designed to selectively recover co-leached mercury from either heap leach pregnant solutions at ambient temperature and low mercury concentrations, or electrowinning pregnant solutions at elevated temperature and high mercury concentration, without affecting gold or silver recovery. The process utilizes a highly selective adsorption-desorption step in which mercury is removed quantitatively by the HgFree adsorbent without adsorption of gold, silver or other metals present. Development of the original HgFree adsorbent has resulted in a process whereby mercury can be recovered as an inert salt and is never present as the free metal. The HgFree adsorbent can be regenerated and recycled in situ, and is capable of being reused multiple times. The overall process is compatible with existing gold mining and recovery practices and offers significant environmental and sustainability benefits, including reduction or elimination of the need to retort mercury with a subsequent reduction in potential mercury air emissions. Development of the HgFree adsorbent and process will be discussed along with a pilot operation at two operating mines.INTRODUCTIONMany gold ore bodies contain high concentrations of mercury which when extracted with cyanide, co-extract with the gold and other metals. This mercury is carried through the process with the gold, posing environmental and technical issues when it is separated from the doré. This paper describes a method to selectively adsorb mercury from the gold recovery circuit while it is in a soluble form, leaving gold to be processed as normal. The removal of mercury from the circuit eliminates the need for mercury retorting of doré and so reduces the potential environmental impact of fugitive emissions of elemental mercury."

Jan 1, 2016

By R. G. S. Mussi

An inclined cooling plate is utilized as a modification in the compocasting process of magnesium alloy and the mechanical properties of the composites obtained are studied in this work. Based on crystal separation theory, molten AZ91D is poured onto an inclined plate in order to produce solidification nuclei inside the fluid metal, and is mechanically stirred while reinforcement is added. Particulate SiC was utilized as reinforcement in quantities varying from 0 to 15%vol. Dispersion of the reinforcement was observed by macro and microstructure analysis. SiC was properly mixed into matrix until 15%vol., and Vickers hardness tests were carried out for the composites produced. Results obtained for hardness were shown to increase with reinforcement addition and comparable to those of traditional compocasting. Utilization of Inclined Cooling Plate produced good inclusion and homogenization of SiC through an AZ91D matrix, at lower temperatures and shorter times than traditional compocasting.

Jan 1, 2006

By Minghui Li

China is the largest coal producer in the world. In 2012, the coal production in China is 3.65billion tonnes, accounting for approximately 49% of global coal production. The raw coal production in 2012 was 3.8% more than the year 2011. 56% of total raw coal has been washed. The increase in raw coal production also promotes technology to be developed and brings separation capacity become larger and larger in coal processing in China. At present, over 40 extra-large scale coal preparation plants (each plant has capacity of more than 10 Mtpa) are in operation in China, the largest one is 32.5 Mtpa. Heavy medium separation are widely used in new built coal preparation, the washing limit for thermal coal feed lower and lower, the equipment selection tends larger which brings the whole washing system simplified, the local equipment developed and manufactured are more and more used. By discussing designs of several typical thermal coal preparation plants and coking coal preparation plants in China, this thesis introduces the current design of China?s extra-large coal preparation plants, and sums up the prevailing design features and trends of extra-large coal preparation plants.

Aug 1, 2013

By Binbin Luo, Northeastern University, Chuanyao Sun, Jie Liu, Yimin Zhu, Yanjun Li

"A series of new type collectors a-bromo-saturated fatty acids, CH3(CH2)5CHBrCOOH (a-BHA), CH3(CH2)7CHBrCOOH (a-BDA), CH3(CH2)9CHBrCOOH (a-BLA), CH3(CH2)11CHBrCOOH (a-BMA) were synthesized from saturated fatty acids and bromine by solvent-free method (Hell-Volhard-Zelinski reaction) in laboratory. The micro-flotation tests of quartz mineral were conducted at a relatively low temperature of 15 °C. The adsorption mechanism of such collectors on quartz mineral surface were established by zeta potential measurements, in conjunction with the results of quartz micro-flotation tests. The flotation results showed that the collecting ability is in the order of a-BMA > a-BLA > a-BDA > a-BHA for the flotation of quartz mineral, which also demonstrating that the a-bromo-saturated fatty acids (a-BFAs) are new selective collectors for reverse flotation to remove quartz mineral from iron ores at a relatively low temperature.INTRODUCTIONThe requirement of higher pulp temperature to maintain the activity of fatty acid anionic collectors which have been widely applied in technological process of iron ores reverse flotation lead to a great deal of energy consumption.The purpose of this paper is to synthesize a new modified collector with carbon chains from eight to fourteen atoms, with strong electronegativity bromine atom introduced into a-carbon position to improve the activity and solubility of the reagent so that it can be adopted at a comparatively low pulp temperature. The collecting performances of these new collectors on quartz surface were studied, and the structure - properties were discussed in light of zeta potential measurements and quantum chemistry calculations."

Jan 1, 2016

By P. S. Arthur

The copper I SAS MELT? process is a submerged lance bath smelting technology. In the 20 years since the process was first demonstrated on a semicommercial scale at Mount Isa in north-west Queensland, Australia, copper ISASMELT? plants have been constructed to treat concentrates or secondary raw materials around the world. The process is operating in smelters in Australia, the USA, Belgium, India, Germany, China and Zambia. ISASMELT? plants have been installed to improve the environmental performance of operating smelters and reduce costs for smelting companies. A new copper furnace is being commissioned at Southern Peru Copper Corporation in early 2007, while more furnaces are under design for installation in Kazakhstan and Peru. Copper ISASMEL T? plants are supplied as complete technology packages including engineering design services for the furnace and key ancillaries, supply of core equipment, provision of intensive training programs in operating plant environments and commissioning assistance services. The proven technology transfer process ensures successful implementation of submerged lance bath smelting into large scale plants. This paper summarises developments at recently constructed copper ISASMELT? plants.

Jan 1, 2007

By Oakley B. Gwillam

The study of leached outcrops as an aid in determining the character of mineralization beneath the surface is in its infancy. Practically all the work on this subject up to the present has been applied to the 'porphyry' copper deposits of the southwestern United States. Some work has been done also on the zinc-lead solid sulphide deposits of the western United States. The question has been asked, "Can this study be applied, and would it have any practical application, in northern Manitoba?" When one realizes the size of the unprospected territory in this Province and the consequent need for a cheap and rapid method of interpreting the countless outcrops which occur in order to discriminate between valueless iron sulphides and valuable sulphides of the base metals, it is readily seen that the study is of great value if it can be applied with a reasonable degree of surety. Augustus Locke, well known economic geologist of the southwestern United States and a pioneer in the study of leached outcrops of disseminated copper ore, has written much on the subject. Messrs. Blanchard and Boswell in a series of articles have dealt with the leached outcrops derived from lead and zinc sulphides in the western United States. Since this paper is essentially a comparison between the leached outcrops of the southwestern United States and those of northern Manitoba with the purpose of testing the adaptability of the study in this Province, an outline of the criteria used in the southwest will be of value to the reader.

Jan 1, 1930

By N. K. Jaber

The "Pidgeon Process" for the extraction of magnesium from dolomite ore utilizing ferrosilicon as the reducing agent has been studied extensively by active metallurgists such Mr L,M, Pidgeon the father of this process, Most of the work sited so far has focused on heating the (FeSi/MgO,CaO) briquette mix under vacuum in stainless steel retorts by external fuel hydrocarbon heating, In this work Electrical Induction Heating was employed as the heating method whereby the briquette mix was placed in a steel crucible around which an Induction Heating copper coil was wound and placed inside in a stainless steel vacuum tank, It was observed that by virtue of the fast Induction Heating method utilized in the silicothermic extraction process higher reduction temperatures were reached in shorter periods of time due to fast heat transport into the ore charge mix, This facilitated shorter metal reduction times as compared to the conventional fuel heating methods.

Jan 1, 2006

By B. S. Prosser, K. G. Wallace, A. Akansobe

"This paper describes a ventilation project at the Wassa gold mine in Ghana. Golden Star (Wassa) (GSWL), a subsidiary of Golden Star Resources, owns and operates the mine. Golden Star holds a 90% interest in GSWL, while the Ghanaian Government holds the remaining 10% ownership, earning a 5% royalty on the gross revenue of GSWL’s gold production. Construction of the underground mine began in mid-2015 and pre-commercial production started in June 2016. Commercial production from the underground mine was achieved in January 2017. This paper describes the ventilation studies performed to support the initial development and production at the mine. The initial ventilation design included four, parallel surface exhaust fans. Future designs will include booster fans, new primary fans, and additional connections to surface. The paper describes the long-term ventilation planning goals and expectations as the mine achieves a production of 4,000 tpd with truck haulage to surface.INTRODUCTIONThe Wassa Gold Mine is located in the southern portion of the Ashanti Greenstone Gold Belt in Ghana, northwest of Tarkwa as shown in Figure 1. The mine has been in production as an open pit since 1998, with some minor disruptions, but the surface minable reserves have become exhausted and the mine started a transition to an underground operation in 2015. The underground mine was initially developed with twin decline accesses extending from the base of the open pit to the mining areas. The mining method selected was sub-level open stoping with cemented rock backfill. The original production level for the mine was 2,500 tpd with ore and waste transported by trucks hauling in the ramps to surface. In 2017 the production goal was set to increase to approximately 4,000 tpd. This resulted in an increase in the truck haulage fleet in addition to a significant increase in ventilation requirements. This paper describes the ventilation upgrades at the mine as it transitioned from a surface to an underground operation and the adjustments the ventilation system needed to make in order to accommodate a significant increase in production"

Jan 1, 2019

By V. Bondarenko

The importance and necessity of gas hydrates deposits development followed by natural gas extraction is considered in the present paper. Analysis is given to world sources focused on methane hydrates formation conditions. Information covering the most perspective gas hydrate deposit of the Black Sea is presented in the article. Two most common methods of gas hydrates development ? thermo stimulation and inhibitor injection are analyzed presenting their comparative characteristics. Basic scientific trends and developments of underground mining department in the field of gas methane extraction from gas hydrates are scrutinized. Schemes and methods of natural gas hydrates development are shown together with formulas, parameters and factors influencing the extraction process. Also the analysis is given to the possibility of gas hydrates formation from methane-air mixtures of degassing wells from coal mines of Ukraine. Improved experimental unit for gas hydrates formation under laboratorial conditions is presented with its basic characteristics. General conclusions and basic tasks requiring further research are given in the end.

Aug 1, 2013

By K. E. Waters, E. R. L. Espiritu, G. R. da Silva

"Rare earth (RE) elements are essential components of emerging green technologies. The increase in demand for these applications have driven the search and development of new rare earth deposits such as the Niobec project in Quebec, Canada. This deposit consists primarily of dolomite with significant amount of RE minerals bastnäsite and monazite, the primary sources of RE elements. Due to the minerals’ fine liberation sizes, flotation is commonly used as a concentration method. To develop an efficient process, the electrokinetic properties of the minerals must be understood. In this study, the surface properties of bastnäsite, monazite (RE minerals) and dolomite (a common gangue mineral) were investigated by zeta potential measurements. These measurements are affected by various ions present in solution; for bastnäsite, monazite and dolomite, some of these ions are H+, OH-, PO43- and CO32-. Dolomite, being a sparingly soluble mineral and a primary component of the ore, may be the greatest contributor of these ions in solution in the form of CO32- ions. Thus, different sources of CO32- ions (from dolomite dissolution and from Na2CO3) were investigated. The research work aims at elucidating how these reagents may influence the minerals’ surfaces. The results have shown that dolomite supernatant and sodium carbonate greatly affect the electrokinetic properties of each minerals. The addition of dolomite supernatant have resulted to relatively similar zeta potential of the minerals; while, sodium carbonate have affected them differently. These observations could be useful in efficient flotation of bastnäsite and/or monazite from bastnäsite-monazite-dolomite system.INTRODUCTIONThe increase in the demand for rare earth (RE) elements has driven the search and development of new deposits. Out of 53 rare earth projects in the world, 19 can be found in Canada (Hatch, 2015). These include the Niobec project of Magris Resources Company in Quebec. This deposit contains a significant amount of rare earth minerals (such as bastnäsite and monazite), with carbonates (such as dolomite) as the primary gangue minerals."

Jan 1, 2016

By T. Guan, G. Fu, X. Zhou, L. Deng

"One kind of tailings from gravity separation of polymetallic mine contains 0.5–0.8% SnO2. The proportion of –0.037 mm size fraction of the tailings is 37.12%, and the distribution rate of SnO2 is 60.32% in it. For this tailings, two processing technology was carried out. One was felt-shaking table gravity separation in which the concentrate with a grade of 30% SnO2 at a recovery of 10% was obtained. Another was flotation-gravity separation in which the concentrate with a grade of 51.20% SnO2 at a recovery of 51.69% was obtained, but the dosage of collectors was as much as 990g/t. Therefore, the experimental research on the influence of grain size composition on the cassiterite recovery were conducted. The results show that: (1) the flotation recovery of the cassiterite distributed in +0.043 mm size fraction is only 10%, flotation recovery is not suitable for it; (2) a portion of cassiterite distributed in –0.01+0.005 mm size fraction could be recovered by flotation, but the tin flotation performance will be worsened rapidly and the dosage of collectors will be increased due to the increase of the content of –0.010 mm size fraction; (3) flotation processing is not suitable for –0.005 mm size fraction of the tailings. According to the results, a new technology has been carried out, that is discarding tailings by gravity separation-hydrocyclone desliming-flotation-gravity separation processing flow. The processing index is close to that of the flotation-gravity separation processing flow, and the collector dosage is decreased to 360 g/t by this processing technology. And, it has been achieved that the cassiterite slime is recovered economically and reasonably.INTRODUCTIONAs the density of cassiterite is higher than that of gangue, gravity separation is considered to be a low cost, pollution free, and effective process for cassiterite recovery (Wills, 2009). However, cassiterite is a kind of fragile mineral, over crushing is easy to take place and a large amount of slime is inevitably produced in the crushing and grinding of cassiterite. For the cassiterite slime exists in –0.043 mm size fraction, the efficiency of gravity separation decreases sharply. The production practice shows that, for the fine cassiterite, the recovery of tin exists in –0.043 mm +0.010 mm size fraction is about 13% through shaking table gravity separation, and the tin exists in –0.010 mm size fraction is almost impossible to be recovered by gravity separation. If flotation is adopted to recover fine cassiterite, the problems of high reagent dosage, high cost, environmental pollution, and poor economic benefit would take place. Therefore, the recovery of cassiterite slime is a worldwide problem. A key way to increase the utilization of tin resource and increase the economic benefit of tin mines is developing suitable beneficiation process for fine cassiterite."

Jan 1, 2016

By Paul Girard

"The copper property of Madeleine Mines Ltd. is in Lapotardiere and Boisbuisson townships, Gaspe North. The initial find was made in 1964, and subsequently a copper deposit of 5.3 million tons of ore was outlined. The property lies in Ordovician sedimentary and volcanic rocks near the major granite intrusive of the McGerrigle Range. The host-rock is a 300-foot-thick metamorphosed silty shale unit, close to the contact of the intrusive. The structure itself coµsists of a southerly-dipping monocline or the south limb of an anticline, on which a large dragfold has been imposed.Chalcopyrite, bornite and chalcocite are the principal sulphides present in the ore. Of particular interest is the zoning arrangement of these sulphides. The orebody is chimney-like in shape and appears to be a fracture-filling deposit that is genetically related to the granite intrusive and is confined within a highly fractured zone of very brittle rock. The deposit presents features uncommon to any of the other known copper deposits in the Gaspe Peninsula."

Jan 1, 1969

By P. R. Geoffroy

Extensive and Intensive Prospecting As often pointed out, the search for new ore deposits may be carried on along two widely divergent lines. It may be either extensive or intensive. By extensive prospecting we mean a search for mineralized outcrops conducted over large and more or less virgin tracts of land, followed by a test of the practical value of any discovery made, the test being limited to the immediate vicinity of the outcrop. Extensive prospecting, was, in fact, the only policy known to the early prospectors. of the American continent and is still the rule in the remote sections of the Canadian Shield and in the African wilderness. It can be further characterized by the lack of emphasis placed on geological and other technical means as an aid to the search for ore. However, very little virgin ground is left, nowadays, for a man or a company to test their luck, and whatever is left is so remote from the necessary means of development that any new discovery will require considerable delay and expenditures to be amenable to profitable mining. On the other band, a great many of the favourable and still unexplored areas (and this is particularly true in Canada) are overburdened to such an extent that outcrops of bed-rock are extremely scarce and extensive prospecting is nearly impossible. Intensive prospecting, to the contrary, must be understood as a detailed search for ore carried on over limited areas in districts already known to be mineralized and covering regional structures whose relation to mineral deposits bas been estahlis.hed with a fair degree ot certainty. The search for deep-seated deposits in the vicinity of successful mines is a perfect example of intensive prospecting. As a matter of fact, the majority of the geologists employed by the mining industry are engaged in some kind of intensive prospecting.

Jan 1, 1950

By A. Boeing

Rock-breaker automation and remote operation improves the safety and efficiency of mining operations. This article presents an overview of the Rocklogic rock-breaker automation system architecture that provides collision avoidance, automated parking, and remote operation functionality. The system consists of a distributed computer control system that interfaces with sensors attached to the rock-breaker, the rock-breaker hydraulics, and the site infrastructure. We present results of an automated Transmin rockbreaker installed in a production environment at an underground Australian mine site. The system has been in production use for over 900 days during which there have been no reported collisions, and 100% adoption of the remote operation technology. As a result, Rocklogic has significantly improved the safety of rock-breaking operations and reduced the rock-breaking cycle time, thereby improving the sites overall throughput.

Aug 1, 2013

By T. Bednarski, T. McCallum, L. Moya, L. Nsenga, B. Mbao

The accumulation of solids in solvent extraction (SX) circuits can cause problems with the physical and economic performance of the operation. These solids are responsible for the formation of crud, a solid stabilized emulsion containing organic, aqueous, air, and fine solid particles. The build-up of crud in SX settlers can limit SX operation throughput, require plant downtime, lead to higher organic losses, or result in higher aqueous in organic entrainment (all of which can have a significant, negative economic impact). Current practices for crud management are typically reactive. Crud is physically removed after it has been allowed to build to excessive levels in the circuit and processed mechanically using centrifuges or filtration. A new proactive solution has been developed to prevent crud formation and build-up. Low ppm dosage of an additive, ACORGA® CR60, into the pregnant leach solution (PLS) has resulted in reduced crud formation in pilot and commercial scale for a variety of PLS streams. This paper will review results from operations in North America and Africa, covering heap leach, concentrate leach, and agitated leach feeds. INTRODUCTION Crud formation and build-up in solvent extraction (SX) circuits has been a long time topic discussed and claimed to be crucial to the whole hydrometallurgical process (Liu, et al, 2006). Crud formation is present in all SX systems be it copper, uranium, zinc, etc., and Ritcey (1980) defined crud as a stabilized emulsion containing organic, aqueous, and fine solid particles. The ore type and feed composition is a major determining factor of crud formation and typically contains Si, Al, Fe, P, and sulfates (Ritcey, 1980). It typically builds at the interface between the organic and aqueous, but can also be observed as floating crud on the surface of the settler, or bottom crud, which is common to find in circuits treating agitated leach feeds such as in Africa. As crud formation has been unavoidable, many of the current crud management techniques are reactive, allowing crud to form and build in SX circuits. Once it does, it is removed and treated via different mechanical techniques, typically through some type of filtration or three-phase centrifuge, to remove the solids and recover the organic phase trapped within the emulsion (Ritcey, 1980). Automated pumping systems have also been designed and are frequently used in North American operations. The time and capital required to react to crud formation can be an overwhelming aspect to SX operation.

Jan 1, 2019

"The Val d'Or Division now comprises the Lucien C. Beliveau Mine and Concentrator (formerly the Pascalis, described below) and the Chimo Mine. Cambior acquired an initial 50% interest in the Chimo Mine in May 1989 and the remaining 50% in April 1990. Cambior's share of 1989 production was 2121 ounces; the company expects to net 23 750 ounces from Chimo in 1990. Pascalis MineUPDATERenamed the Lucien C. Beliveau Mine at its official inauguration in September 1989, the mine is exceeding forecasts, producing over 11 500 ounces of gold in the first half of 1990. Cambior expects 1990 production to total 34 000 ounces.IntroductionThe Pascalis Mine is located 16 miles east o f Val d'Or, Quebec, and is accessible by a three mile gravel road off highway 117 (Fig. I).The property is wholly owned by Cambior.The Pascalis gold deposit consists o f a sub-vertical diorite dyke 1000 ft long by 30 ft wide containing quartz and tourmaline veins with inclusions of pyrite and native gold . Three vein systems ca n be seen in the deposit , the most important being tensile veins oriented at a right angle to the direction of the dyke and inclined at 40 degrees. These overlapping veins vary in thickness from 4 in. to 40 in. and occur at intervals of six to ten ft. The deposit is, therefore, very difficult to evaluate; a complete evaluation would require drifts over the whole width of the dyke combined with relatively short drill holes (Fig . 2)."

Jan 1, 1990

By N. Sauret-Szczepanski, G. Patry, S. Gauthier, G. Potvin, C. Munger

Adsorption/thermal desorption with sorbent cartridges and analytical method using gas chromatography coupled to mass spectrometry (GC/MS) was developed for the determination of tetrafluoromethane (CF4) and hexafluoroethane (C2F6) emitted from primary aluminum smelters. A customized cartridge was built like a packed column with a stainless steel tube filled with a specific resin. The optimization of adsorption and desorption parameters was carried out to support the PFC sampling for all aluminum production technologies. The proposed method showed good linearity for concentrations ranging from 10 to 500 ppbv for CF4 and from 5 to 500 ppbv for C2F6 with correlation coefficients above 0.999. In certain conditions, the detection limits of the analytical method reached 0.3 ppbv for CF4 and 0.15 ppbv for C2F6- Using this methodology, a field campaign was carried out using a sequential sampler allowing the simultaneous sampling of PFC with cartridges and sampling bags. The results showed no significant difference (t-test) between the two sampling technologies and no breakthrough was observed from the cartridges .

Jan 1, 2006

By J. Gebhardt, D. McBride, C. R. Bennett, Croft. N., M. Cross

A comprehensive model of solution flow through heap leach systems requires a numerical solution with the ability to predict variably saturated-unsaturated flow through porous media domains that contain materials with spatially variable properties. The types of flow associated with stockpile leach processes lead to flow problems, such as infiltration into dry soil, drainage, perched water tables and flow through heterogeneous materials. Computational methods for modelling this class of flow behaviour are conventionally based on the classical Richards' equation. However, the governing equations are highly non-linear, difficult to solve, and require iterative numerical solution methods. The pressure-based form of the Richards' equation suffers from poor mass balance, while the mixed form can possess convergence difficulties. An adaptive transformed mixed algorithm is described, which reduces the non-linearity of the problem, optimizes the time step size, and provides a fast, numerically robust scheme that significantly reduces computation (or CPU) time. This method is shown to give fast, accurate solutions on a number of complex flow problems. The utility of this algorithm is illustrated through its implementation within the PHYSICA computational modelling software, which incidentally, provides a framework for a comprehensive heap leach model.

Jan 1, 2005

By Mahmood Alemrajabi, Ake Rasmuson, Kerstin Forsberg, Kivanc Korkmaz

"In the present study, the recovery of rare earth elements (REE) in the nitrophosphate process of fertilizer production is investigated. The apatite has been recovered from iron ore tailings by flotation. After digestion of apatite in concentrated nitric acid, Ca(NO3)2.4H2O is first separated by cooling crystallization and then the REEs are recovered by precipitation. Optimum conditions in these steps have been determined in a previous study. The precipitate mainly consists of CaHPO4.2H2O and REE phosphates.In the present study, selective dissolution and re-precipitation have been studied in order to obtain a precipitate that is more concentrated in REEs. The precipitate was selectively dissolved in nitric and phosphoric acid at different acidities (pH 6 to 0) with the liquid /solid ratio of 100 mL/g. It is shown that most of the CaHPO4.2H2O and other calcium containing compounds will be dissolved at pH 2 while the REE phosphates are not dissolved above a pH of approximately 2. Thus, by partial dissolution of the REE precipitate at pH 2.5 most of the solid calcium phosphates will be dissolved and the remaining solid phase, which is more concentrated in REEs, can be filtered off as a fairly concentrated REE solid mass and the liquor can be recycled back to recover more P nutrients. Alternatively, the REE enriched precipitate was dissolved completely in nitric acid and re-precipitated again by addition of ammonium hydroxide to pH 1.2. A chemical equilibrium software, MEDUSA (Puigdomenech, 2013) has been used to evaluate the experimental results and to estimate the optimum conditions for selectively dissolving the precipitate."

Jan 1, 2016