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By W. R. Reed, D. E. Pollock, T. W. Beck, J. A. Organiscak, J. D. Potts

In underground continuous mining operations, ventilation, water sprays and machine-mounted flooded-bed scrubbers are the primary means of controlling respirable dust exposures at the working face. Changes in mining arrangements — such as face ventilation configuration, orientation of crosscuts mined in relation to the section ventilation and equipment operator positioning — can have impacts on the ability of dust controls to reduce occupational respirable dust exposures. This study reports and analyzes dust concentrations measured by the Pittsburgh Mining Research Division for remotecontrolled continuous mining machine operators as well as haulage operators at 10 U.S. underground mines. The results of these respirable dust surveys show that continuous miner exposures varied little with depth of cut but are significantly higher with exhaust ventilation. Haulage operators experienced elevated concentrations with blowing face ventilation. Elevated dust concentrations were observed for both continuous miner operators and haulage operators when working in crosscuts driven into or counter to the section airflow. Individual cuts are highlighted to demonstrate instances of minimal and excessive dust exposures attributable to particular mining configurations. These findings form the basis for recommendations for lowering face worker respirable dust exposures.

Jan 1, 2016

By Rongdong Deng

A tower-like magnetic system comprising eight permanent magnets was installed at the center of a flotation column to separate chalcopyrite and pyrrhotite minerals. A cyclonic flotation was installed within the underpart of the column to separate the pyrrhotite from the gangues. A three-product magnetic flotation column was fabricated to create a magnetic field and a cyclonic zone. The products were Cu concentrates, pyrrhotite concentrates and tailings. The theoretical magnetic field strengths and the magnetic forces were calculated. The results of the flotation experiments showed that the Cu grade increased from 14.20% without the magnetic field to 26.40% in the presence of the magnetic field and that the S grade in the pyrrhotite concentrates increased in the presence of cyclonic flotation. The separation efficiency of this magnetic flotation column was evident. Therefore, this three-product magnetic flotation column may have a potential application, due to its high separation efficiency.

A comparison of gold, platinum and sulfide ion selective electrodes was made in this investigation for determination of Eh in solutions containing sulfide ions as a model system. The comparison was made in terms of the accuracy of the measured response, response time, pH dependence, and reproducibility of measurement. In addition, the sensitivity of each electrode towards changes in sulfide ion concentration was measured in terms of the change in measured Eh per decade change in concentration of sulfide ions. On the basis of a detailed investigation of the electrode processes occurring at the surface of gold and platinum electrodes, it was postulated that within the pH range investigated these electrodes respond to changes in the hydrosulfide ion, HS-, concentration in solution. In comparison, the sulfide ion selective electrode is known to respond to changes in the sulfide ion, S-, activity in solution. Although the potentials measured with gold and platinum electrodes were mixed potentials, pretreatment procedures can be used to obtain a signal suitable for process control. For control of sulfide ions in flotation pulps, the use of a gold electrode pretreated at 1.0 V with respect to a standard hydrogen electrode is recommended.

Jan 1, 1990

By T. C. Page

The Yarnell gold depoSit, located in the Weaver mining district of Yavapai County, Arizona is found within a structurally controlled, hydrothermally altered zone that occurs within a 1700 Ma granodioritic intrusive. Both potassic and sericitically altered rock that occur around and above the low-angle northeast striking Yarnell fault are known to host economic gold mineralization; a wider envelope of weakly-propylitic alterred rock also occurs in this area. During mineralization, strong sericitization accompanied several stages of quartz ± adularia veining, stockwork formation, and localized silicification and potassic replacement, in association with deposition of specularite, pyrite (now oxidized), and gold. The footwall of the fault is also sericitically altered but poorly mineralized. Mineralization along the Yarnell fault continues both northeast and southwest from the main deposit although the thickness of the zone and associated alteration envelope diminish away from the orebody. A sample of undeformed illite taken from the Yarnell fault zone was K/Ar dated at 69 ± 1.6 Ma; this date reflects a minimum age for both mineralization and latest movement on the fault. Gold mineralization is accompanied by modest increases in Ag, As, Cu, and Mo content. Both CO2-and H20-rich fluid inclusions were studied and suggest mesothermal pressures and temperatures of formation for the deposit.

Jan 1, 1992

This one day field trip is sponsored by the Denver Region Exploration Geologists? Society, May 14th 2009. The trip highlights major geologic features and some notable uranium occurrences along the north-south mountain-basin boundary southwest of Denver and continuing north to Fort Collins, Colorado. Uranium deposits visited include sandstone?hosted roll front type and polymetallic veins hosted in metamorphic rocks. A replacement ?episyenite? type occurrence is considered via description and hand samples but is not visited owing to logistical constraints. Recovery methods addressed include underground mining and in-situ leach recovery. Samples of Precambrian basement rocks, deposit host rocks, uranium ore samples, and ore polished sections viewed by reflected light microscopy will be available. A road map showing the locations of the stops serves as the front cover of this field guide. The Robinson episyenite-hosted occurrence (not visited) is labeled as Stop 6. A stratigraphic column is provided which shows the position of the host rocks at each stop (Figure 1-1).

Jan 1, 2009

By A. Moharana

A massive slide at Bingham Canyon wiped out a side of the pit and covered the main haul road in and out of the pit. All pre-slide mine designs and schedules were no longer valid. New designs and schedules needed to be developed quickly to provide management with information regarding the immediate post-slide production potential and the time needed to ramp back up to full production. At the time of the slide, an effort was already underway to convert Bingham?s in-house Medium Term Scheduling Process to MineSight®?s Schedule Optimizer (MSSO). One of the main reasons for doing this was to reduce the time needed to produce Medium Term Schedules at Bingham, which involves a complex shovel-based scheduling approach with shovel productivities based on shovel type and the types of mining cuts to which the shovel is assigned over each planning period. The objective of the schedule was to maximize shovel usage, satisfy mill feed requirements of four SAG mills with variable milling rates, and have flexibility in setting truck constraints. This paper will describe how the new MSSO-based mine scheduling process met the challenge of producing new schedules for Bingham in a minimal amount of time.

Feb 23, 2014

By William S. Alldredge

The Washington Metropolitan Area Transit Authority(WMATA) officially came into existence in February 1967 after the District of Columbia, Maryland, and Virginia joined in a com¬pact pursuant to Federal creative legislation signed the previous November to build a regional rapid rail transit system called METRO (1). The parent organization was the National Capital Transportation Agency (NCTA), a Federal agency, subject to Federal statutes and regulations. Soon after the completion of the transition from NCTA to the new "non-Federal" status of the Authority, the Board of Directors of the Authority formally adopted procurement policies and procedures (2). These are specific statements concerning competition by formal advertising for bids or by solicitation of proposals for negotiation, contracting authority, approval of awards, awards of contract modifications, and processing of claims and disputes. These policies and procedures are silent as to Federal procurement statutes and regulations. But because of the Authority's origin, the sensitive nature of the compact among the several sovereign jurisdictions, Federal financing of two-thirds of the costs, and the resultant surveillance by the General Accounting Office over staff operations, the Authority's procurement practices follow closely Federal regulations adapted to WMATA's needs. This is an important point and is the foundation of contractual relations between the Authority as the owner and its construction contractors. Various constraints and flexibilities of this arrangement with respect to excavation and tunneling contracts will be pointed out in the ensuing discussions.

Jan 1, 1974

By Ali Kazmi, Wern-ping N. Chen

A load rating procedure was performed to evaluate safe load capacity of the Port of Miami Tunnel (POMT), FDOT Tunnel No. 871071 SR 887. The rating procedure performed on a total of eleven stations beneath roadways and with fill depth less than the tunnel exterior diameter (42 ft). Calculations on tunnel sections passing beneath roadways were performed to evaluate the structural response of the sections subject to moving vehicular loads, dead load, and earth pressures. Ratings were performed in accordance with AASHTO and FDOT guidelines. The procedure considered two types of vehicles (HL-93 and FL-120) and two rating levels (Design level and Permit level). As part of HL-93 vehicle, Tandem load was also considered for rating, separately. For HL-93 and HL-93 Tandem, inventory and operating level ratings were performed. The results show rating factors are high. The minimum rating factor is 16.8 using Inventory truck HL-93. For Permit level using FDOT FL-120 truck the minimum rating factor is 6.9. As can be seen, rating factors are higher than comparable analysis for bridges. This paper explains how the procedure can be implemented for tunnels and evaluates the rating results.

Dec 1, 2022

By S. I. Angadi, C. Eswaraiah, Sunil Kumar Tripathy, T. Santosh, Nilima Dash

Banded hematite quartzite (BHQ) and banded hematite jasper (BHJ) ores represent a promising potential iron ore resource in the near future. The hematite and quartz in BHQ and the hematite and jasper in BHJ are closely related and require fine grinding for the liberation of hematite phases. The present study investigates the mineralogical features and comminution properties of BHQ and BHJ ores. In the BHQ ore, it is observed that thick bands of hematite have fine inclusions of silicate minerals, whereas silica bands have few grains of iron-bearing minerals. The hematite and quartz minerals in the iron and silicate bands of the BHJ ore appear to be more intricately associated and complex in nature, presenting difficulties for liberation. Bond work index studies were carried out for the BHQ and BHJ ores with different product fineness in order to evaluate the energy requirements in fine grinding. A higher Bond work index value was found for the BHJ ore (15.4 kWh/ton) than for the BHQ ore (12.4 kWh/ton). A decrease in the product particle size was associated with an increase in the work index value. Single-particle breakage experiments were designed by varying feed particle size and input energy. The specific energy consumption for the BHJ ore was higher than that for the BHQ ore. The comminution parameters showed that the BHJ ore is harder to grind than the BHQ ore, which may be due to the mineral composition and association of hematite phases with the silicates.

By S. A. Smith-Hamm, E. A. Sarver, A. S. Cox

Appalachia is an increasing concern, as unnaturally high TDS and/or associated specific conductivity (SC) may contribute to deteriorated stream ecosystem health. The aim of this preliminary study was to explore the efficacy of accelerated leaching as a means of minimizing long-term TDS/SC generation by problematic overburden materials. Five spoil samples were collected and leached using simulated rainwater solutions under ambient and acidified pH conditions. SC and pH were monitored during each leach cycle, and inductively coupled plasma-mass spectroscopy (ICP-MS) was used to determine how leaching conditions affected the release of specific ions. This paper highlights the results of both jar and column leaching tests. Among the most significant findings was that for certain spoil materials, the SC in the leach column effluent was effectively reduced when the spoil was first leached with acidic rainwater followed by ambient rainwater, as opposed to leaching with ambient rainwater alone. This suggests that accelerated leaching might aid in the long-term stabilization of some materials.

Jan 1, 2015

By J. Andrew McGlenn, Greg Emslie, Murray Gant

The Second Narrows Water Supply Tunnel will ensure system reliability in the event of a major earthquake and increase the Greater Vancouver Water District’s capacity to meet a growing population’s longterm needs. It includes a bored tunnel between two deep shafts located in North Vancouver and Burnaby, BC, Canada. The support of excavation for the 16-meter-diameter (52.5 ft) TBM launch shaft consists of 83-meter-deep (272 ft) unreinforced concrete slurry walls. This paper discusses challenges encountered during construction of the launch shaft slurry walls, namely excavation methods and slurry loss, and mitigative solutions implemented to successfully complete the shaft with minimal impact to project schedule.

Dec 1, 2022

By J. F. Power

Returning the original soil material to the surface of smoothed mine spoils is n practical means of restoring agricultural productivity. Research has established that high-sodium spoils in North Dakota (a) must be covered with about 70 cm of soil material to achieve maximum production; (b) topsoil must be segregated and spread separately from subsoil; (c) potential production depends on the quality of the soil material returned; and (d) erosion and upward salt movement must be controlled for sustained production. Erosion is best controlled by reducing final grades as much as possible during the smoothing process followed by prompt establishment of vegetation. Almost half the nation's cool reserves are in the Northern Great Plains underlying several million hectares of agricultural land. Social pressures to return mined land to agriculture or other productive uses have resulted in recent enactment of state and federal legislation, which is intended to restore productivity to disturbed areas. All such legislation relating to the Northern Great Plains has stipulated that useable soil material be saved and returned to mined land after spoils are smoothed. This requirement immediately raises questions as to how much soil material is needed, what criteria are important in defining useable soil material, how is the soil material to be handled in the earth-moving operations involved, and how can replaced soil material be maintained and revegetation. Scientists at the USDA Northern Great Plains Research Center at Mandan, North Dakota have conducted research on the reclamation of disturbed lands since 1970. Initially this research was designed to identify and characterize those physical and chemical properties of spoils that are most restrictive to plant growth (1). Basically, they found that any properties of spoils that reduced the efficiency of storage and utilization of the limited precipitation received adversely affected plant growth. Thus, in the Northern Plains, revegetation of mined land was found to depend upon the management of factors affecting the availability of water to plants - the same as on unmined land. After the major problems in revegetation were identified, technologies were developed to circumvent the effects of the growth-limiting factors (2). Basically two approaches were identified by which plant growth-restricting properties of spoils could be corrected: (a) various amendments (gypsum, sulfur, Fertilizers, mulches, calcium chloride, etc.) could be applied to spoils to improve their ability to conserve precipitation and provide water for plant growth; or (b) undesirable spoils could be covered with suitable soil materials to reduce or alleviate adverse effects. The latter approach appeared to be more feasible in most instances And is the approach specified in current legislation. The remainder of this paper discusses research on the use of roil materials returned to spoils and summarizes the information obtained.

Jan 1, 1978

By Arthur B. Cummins

It is appropriate to discuss diatomite at an AIME meeting in San Francisco. California has led the nation, and the world, in the production of diatomite products for more than 40 years. It appears that our State will maintain this position for a long time to come. Diatomite today ranks high in the list of California mineral commodities, with a total value since 1889 well in excess of $100 million. California's production has more than doubled since 1942. In 1959, the value of diatomite production in California is exceeded only by the following industrial mineral materials-borates, stone, sand and gravel and cement20,28. Also, not unimportant is the production of diatomite in each of our other Pacific Coast States, including Nevada. First, let us define diatomite. It is a sedimentary siliceous rock of organic origin, which consists mainly of the fossilized remains of diatoms. Diatoms are microscopic aquatic plants which have the capacity of precipitating silica bio-chemically so as to form a part of their organized structure. In the economic sense, we are not concerned with the numerous types of sedimentary materials which contain minor amounts of diatom residues, or with impure or highly indurated siliceous materials, which may have been formed from diatomite2. Diatomite (synonyms--diatomaceous earth, kieselgurO is a term generally restricted to material of such qualities as to be suitable for commercial uses. Diatomaceous silica is a designation which is best used to distinguish the basic component of diatomite, that is, the substance of the silica shell itself, and which is the major' constituent of beneficiated diatomite or processed diatomaceous products.

Jan 1, 1959

By Richard E. Beane

For several decades, the minerals industry has used leaching techniques to extract metals from rocks whose grade was too low to be treated profitably using conventional metallurgical techniques, and, as of 1972, about 15% of domestic copper production was derived using leaching methods (Beall 1). Increasing interest is currently being directed toward solution mining, particularly with respect to copper, for basically two reasons. In the first place, geological exploration has outlined several copper deposits of large tonnage and 1m', grade which are buried at sufficient depth to preclude open-pit mining which would make such mineral deposits ore deposits. Nevertheless, these occurrences provide significant potential if they could be treated by chemical leaching in situ. Secondly, the porphyry deposits of the western united States, which provide by far the largest percentage of domestic copper, do not terminate geometrically with sharp borders. These large disseminated bodies commonly decrease in grade laterally away from volumes of rock containing ore grade metallization, and the distinction between ore and waste is strictly economic. In order to extract ore grade material from the ground, a significant amount of rock containing sub-ore-grade copper must also be removed which, when placed on dumps, is amenable to solution mining. These two considerations clearly indicate the reasons for the growing interest in solution , leaching techniques--namely the ability to exploit deeply buried low grade deposits and the expansion of reserves in deposits currently under production.

Jan 1, 1977

By Edward C. Mabbs

U.S. industry must increase its productivity or lose its competitive position in the rapidly expanding and inter-dependent world markets. Recent improvements in material handling techniques and equipment, coordinated with production processes, provide one of the greatest opportunities to increase productivity. Successful managers must learn how to take advantage of these material handling opportunities to gain competitive position.

Jan 1, 1973

By E. Costa Silva

Among the methods of mineral processing, gravity concentration methods are, probably, those which have lower costs, higher capacities and lower operational complexity. In order to be really effective, these methods require a feed size distribution in which the particles are liberated. Further, there must be a significant difference (usually higher than 1-1.5) among the real densities of the particles. However, in most cases, the traditional gravity concentrators (jigs, shaking tables, spirals and dense medium hydrocyclones) lose efficiency (sharpness of cut and recovery) when the mean diameter of particles are lower than 0.05mm and the difference among densities are smaller than 1. Most gravity concentrators developed in the last 20 years are based on the use of centrifugal forces that create large "apparent gravitational gradient" seeking to overcome the limitations of particles size distribution. This paper presents the experience of the CVRD Research Center in evaluation and development of new process based on using this new generation of gravity concentrators.

Jan 1, 1999

By J. Stawovy, A. Fourie, J. D. Quaranta

Coal refuse impoundments are disposal facilities specifically designed for the coal mining industry. Re-purposing refuse impoundments for co-disposal with natural gas flowback water and waste rock overburden has been investigated. The aims of this study were to investigate properties of coal refuse classification under the influence of co-disposed wastes as geochemical material exposure pathways from hydraulically exposed sodium and calcium ( Na+, Ca2+) cation loading from disposal of flowback water produced during the development of horizontal drilled natural shale gas frack wells, and waste rock having limestone characteristics. The geotechnical index classification of saturated cohesionless refuse is required to evaluate the liquefaction potential for strain or strength loss contributing to ground movements. This study is relevant to identifying changes in the coal refuse geotechnical index classification as sand-like, clay-like, or a borderline transitional material from the effects of ion and waste exposure in the impoundment’s reservoir porewater. Laboratory geotechnical tests were performed on fine coal refuse blended with different cations to classify the altered plastic behavior and index classification. Following determination of the index classification, the specimen’s stress–strain responses were investigated through isotropically consolidated undrained (ICU) triaxial compression tests. This experimental study culminated with two salient findings: the first is that introduction of ions alone into the refuse tailings or impoundment porewater resulted in significant material changes in property index classification, and the second finding was that the difference in refuse index classification did not correlate into noticeable effects of the monotonic undrained triaxial strength parameters.

Jul 5, 2022

By L. Xia, B. Hart, V. Sidorkiewicz

Sodium silicate(s), also known as “water glass”, are one of the oldest and most widely used industrial chemicals. Its first use in North American mining operations can be traced back to around 1925, which coincided with early use of xanthates in mineral flotation. Silicate functions as a sulphide and non-sulphide gangue mineral dispersant, depressant and modifying reagent in grinding and flotation operations. It is believed that soluble sodium silicate promotes selectivity of value added sulphides against gangue minerals, resulting in both grade and recovery improvement. This paper seeks to link improved grade/recovery to the interaction characteristics of minerals and the sodium silicate. A systematic study was performed with individual mineral species, an artificially designed model ore and the feed ore from a copper metallurgical operation. The function of sodium silicate was evaluated in the context of colloidal chemistry and linked to mineral surface chemistry. Measurement of pulp rheology and mineral zeta potential identified that sodium silicate works as a dispersant. The dispersion is accomplished by increasing a mineral’s net surface charge, resulting in a mineral variable change in viscosity. Bench scale laboratory flotation tests suggest that better dispersion leads to a diminished interaction of chalcopyrite with gangue. The improved Cu grade and recovery then are likely in response to an increased accessibility to collector along with a linked increase in particle bubble attachment resulting in better separation efficiency. ToF-SIMS surface chemical analysis of the flotation samples found a higher proportion of sodium silicate on minerals from the flotation tailings relative to the concentrates. Moreover, attachment of sodium silicate appears to be mineral specific; the data indicates that sodium silicate favours the surface of gangue phases over the value sulphides. INTRODUCTION Mineral processing involves enrichment of valuable minerals from an ore, where the separation process utilizes differences between the properties of the value-added and gangue minerals. The properties of minerals, for example composition, specific gravity, particle size, magnetic properties etc., in any flotation feed ore, can vary significantly between the various minerals present. In flotation seperation surface chemistry and wettability is a significant component promoting selective separation of the various mineral phases [1,2] Mineral surface wettability can be changed, advantageously or deleteriously, by many factors including: surface layer alteration through oxidation; galvanic interactions; attachment of secondary precipitates; the adsorption of various reagents [3] In the flotation context the wettability of a minerals surface can be manipulated by various reagents. Collector reagents may selectively attach to specific minerals in the mineral/water slurry enhancing their surface hydrophobicity, increasing bubble-attachment efficiency and improve flotation kinetics and mineral recovery [4]. In contrast, depressant reagents may selectively reduce a minerals surface hydrophobicity resulting in poor particle-bubble attachment and non flotation. In essence, a mineral flotation flow sheet is designed to induce/promote a hydrophobic surface to the value mineral and a hydrophilic surface to all others. Therefore, the versatility of the froth flotation process lies in the selection of different flotation reagents.

Jan 1, 2019

By D. E. Cameron

"INTRODUCTION Grade control requirements for base and precious metal projects are an important input to both conceptual and feasibility mine plans. It’s the author’s experience that grade control input is insufficient at these critical stages. The few exceptions are a stimulus for this paper. A significant portion of CRC’s practice has involved assisting operations to solve grade control issues which were finally recognized as contributing to negative production variances. Even in operations perceived to be successful, deficiencies in grade control are often masked by measures taken by an operation to compensate a deficiency in one area with outperformance in another. The advantages in having a realistic and adequate grade control plan developed at an early project stage by a geologist(s) with considerable operations experience are manifold. It’s important for the geologist to prepare clear inputs into the mine plan backed by detailed supporting information in usable, flexible formats. When the decision is made to advance a project, the exploration team passes its model to a mine planner. The team doesn’t usually provide a detailed grade control plan with the block model, thus the planner tends to treat grade control as an activity to be rolled into a broader operating category. The consequences of highly compartmentalized mine planning can be severe in the long run. Once a plan is tabled, and especially once production begins, it is very difficult to improve grade control outside the fixed parameters of the operation. Major fixes tend to be costly in terms of time and dollars. Implementing needed changes to the grade control practices and culture in an established mine can present almost insurmountable difficulties. Hypothetical examples of grade control planning are presented to illustrate the author’s points. The diagrams are conceptual and schematic; any resemblance to actual deposits is coincidental. BEYOND 50¢/TON In more than a few cases, grade control cost is buried in a subcategory of mining cost with little more consideration than a plugged number. It is possible to do a word search in 43-101 Technical Reports on advanced projects and without finding reference to “ore control” or “grade control”. The idea is to reach the orebody by the shortest and least expensive means, achieving production and investor payback at the earliest possible occasion. This entails a low stripping ratio pit or a decline ramp with sills on ore to prepare the first stopes. The processes to achieve the target production, one of which is grade control, will fit into this framework. After all, there is a block model and the planner can see the grade and tons in each block. The exploration geologist whose responsibility was to bring a large percentage of the deposit into mineral resource owns the model and has released it to planning. Now comes the planning stage. Mine geologists haven’t been hired yet and they will be phased in with production. What could go wrong? Larger companies may have the geologists with operating depth who will be inserted into the mine planning discussions, but it’s not a given. Junior companies must often delegate the conceptual and detailed planning tasks to consultant groups. Is a senior-level grade control review part of the scope of work for the mine planning? If a good grade control plan is in place before the mine geology team is staffed, a key element of success is assured."

Jan 1, 2018

By A. Porvali, V. Agarwal, M. Lundström

Hydrometallurgical recovery of rare earth elements (REE) from NiMH battery waste can be performed using sulfuric acid leaching followed by selective precipitation as double salt (REENa(SO4)2•H2O) by adding Na2SO4 as a precipitating agent. The formed double salts can be treated further with NaOH solution to form REE hydroxides. This study focuses on metamodeling of a simulated flowsheet with design of experiments (DOE). Based on literature survey, a process flowsheet was developed using HSC Sim software. The created flowsheet focuses on circulation of solution containing Na+, K+, SO42- ions and impurities liberated in the NaOH treatment of double salt precipitate. The effect of seven parameters (P1-P7) on seven responses (R1-R7) were modeled using central composite design (CCD). INTRODUCTION Nickel metal hydride (NiMH) battery waste can be considered as an urban mineral due to the presence of valuable metals like: Ni, Co and rare earth elements (REE) (Larsson et al., 2013). In NiMH battery waste leaching experiments, sulfuric acid has often been employed as a lixiviant (Pietrelli et al., 2002,Zhang et al., 1999,Rodrigues and Mansur, 2010,Porvali et al., 2018). The key advantages of sulfuric acid are its stability and cost-effectiveness compared to other mineral acids such as HCl and HNO3. However, the usage of sulfuric acid in NiMH battery waste leaching poses simultaneous challenges and advantages. Limited REE solubility can be taken as benefit when recovering REEs double sulfates after solid-liquid separation. However, sodium and potassium hydroxide, present in electrolyte residues in the battery waste, can cause in-situ precipitation already during leaching due to limited solubility, thus decreasing the total REE recovery (Porvali et al., 2018). However, this problem can be circumvented by washing the electrolyte residues off the raw materials. Subsequently, the REEs may be precipitated in bulk as a mixed double salt out from the solution at very low pH with minimal co-precipitation of Ni and other metals. This relatively easy separation method can be extremely advantageous in the case of such a complex solution matrix with relatively high REE concentrations (conc.). Once REEs have been precipitated as double sulfates as per eq. (1) (Porvali et al., 2018), the resulting double salt precipitate lacks applications without further treatment. Direct thermal treatment would generate sulfur dioxide emissions and likely require high temperatures in order to transform double sulfates into REE oxides. Furthermore, the precipitate contains Na ions, which would need to be removed by chemical treatment from the calcined REE product. In the context of circularity of raw materials, it can be taken of a remarkable benefit if the sodium and sulfur present in the double salt could be reused instead of wasting them into the side streams. To that end, in this simulation study, the double salts are converted by dissolution and precipitation to hydroxides which are readily treatable, e.g. with total dissolution and solvent extraction, for further purification (Abreu and Morais, 2010):

Jan 1, 2019