Hydrometallurgical Operations Research Articles

РH process as a technology for reprocessing mixed uranium–plutonium fuel from BREST-OD-300 reactor

A technology for reprocessing mixed uranium–plutonium nitride fiel (MUPN) from BREST reactor is considered. The technology should ensure reprocessing of spent nuclear fuel with the storage time after irradiation of no more than 1 year, 10–15% content of fissile materials (FM), and burn-up of 10% of heavy atoms. The target product of the technology is a mixture of actinide oxides separated from fission products with the separation factor of ~106. A PH (Pyro–Hydro) process was suggested for MUPN SNF reprocessing. It involves pyroelectrochemical fuel reprocessing with separation of U, Np, and Pu from the major fraction of fission products responsible for the heat release from the fuel and for the radiation load on process media, a series of hydrometallurgical operations for final purification of the target products (U–Pu–Np–Am), and radioactive waste (RW) management. The PH process is being developed since 2011 by the teams from the Bochvar High-Tech Research Institute of Inorganic Materials, Khlopin Radium Institute, and Research Institute of Atomic Reactors with active participation of the Leading Research Institute of Chemical Technology, Siberian Chemical Combine, and institutes of the Russian Academy of Sciences, primarily Frumkin Institute of Physical Chemistry and Electrochemistry and Vernadsky Institute of Geochemistry and Analytical Chemistry.

Magnetite precipitation for iron removal from nickel-rich solutions in hydrometallurgy process

In nickel hydrometallurgical operations, the removal of iron from process liquors was critical, with the method of choice commonly being crystallization (precipitation). In this paper special attention was given to the magnetite precipitate. Potential/pH diagram for Fe–H2O system was derived at 100°C, and indicated that the iron ion may precipitate as magnetite at the lower oxidation potential. And the crystallization experiments proved that the iron ion partly precipitate as magnetite by slow oxidation at pH2.0–2.2 and temperature 90–100°C. The precipitates could be efficiently separated from the solutions by magnetic flocculation and separation. Further, analyses with Environmental scanning electron microscopy (ESEM) and X-ray Diffraction (XRD) provided a fundamental understanding of the magnetite precipitation process.

The effect of fluid rheology and medium on the performance of a helical ribbon mixer for concentrated manganese nodule slurry

ABSTRACTIn hydrometallurgical and mineral processing operations, slurries are often prepared at very small grind sizes and high solids concentrations. The presence of yield stress or flow limits results in flow anomalies as the slurry tends to stagnate close to vessel bottom, walls, and at any internal surface. The preparation of high-concentration slurries preferably in low shear rate ranges consuming less power is an integral part of high-concentration slurry transportation systems. Therefore, during mixing of such concentrated slurries, the selection of appropriate agitation equipment for preparation of a homogeneous suspension requires a thorough investigation. The rheological behavior of ground manganese nodule samples in solids concentration range of 55–65% by weight using both distilled water and sea water as mediums have been evaluated and the discrepancy in yield stress and plastic viscosity values affected by solids concentration and medium has been discussed and presented in the paper. The performance characteristics of a helical ribbon mixer influenced by fluid rheology, medium, and agitator rotational speed were evaluated. The appropriateness of the agitator for preparation of high-concentration manganese nodule slurry was further substantiated by comparing the experimental power consumption data with the theoretical power consumption values computed using Bakker and Gates correlations.

Demonstration Plant Equipment Design and Scale-Up from Pilot Plant of a Leaching and Solvent Extraction Process

Germanium recovery from coal fly ash by hydrometallurgical procedures was studied at the pilot scale (5 kg of fly ash/h). Results were used to design the equipment of a demonstration-sized plant (200 kg of fly ash/h). The process is based on hydrometallurgical operations: firstly a germanium extraction from fly ash by leaching and a consequent Ge separation from the other elements present in the solution by solvent extraction procedures. Based on the experimental results, mass balances and McCabe-Thiele diagrams were applied to determine the number of steps of the solvent extraction stage. Different arrangements have been studied and a countercurrent process with three steps in extraction and six steps in elution was defined. A residence time of 5 min was fixed in both the extraction and elution stages. Volumetric ratios in extraction and stripping were: aqueous phase/organic phase = 5 and organic phase/stripping phase = 5, so a concentration factor of 25 is achieved. Mixers and decanters were completely defined. The maximum extracted and eluted germanium was estimated and a global efficiency of 94% was achieved. The cost-effectiveness of the equipment was estimated using the Lang factors.

Uranium Extraction Studies Employing Tributyl Phosphate and N,N-Dihexyl Octanamide as Extractants: Counter-Current Centrifugal Contactors Runs

Straight chain N,N-dihexyloctanamide (DHOA) has been identified as a promising alternative of tributyl phosphate (TBP) in the reprocessing of irradiated uranium based fuels. This article deals with the evaluation of DHOA vis-à-vis TBP as extractant in counter-current runs employing centrifugal contactors for uranium extraction from feed solutions of varying compositions such as uranium solutions (20, 50.4 g/L) at acidities (1–4 M HNO3), and simulated Advanced Heavy Water Reactor (AHWR) spent fuel dissolver solution. Experiments were also carried out to recover uranium from assorted organic waste solutions. Dispersion number of DHOA was calculated prior to counter-current runs and compared with different solvents proposed for back-end of fuel cycle. These runs demonstrated that DHOA is a promising alternative of TBP for various hydrometallurgical operations dealing with the recovery of uranium from solutions of various origins including spent fuel dissolver solutions.

Hydrometallurgy in Kghm Polska Miedz SA – Circumstances, Needs and Perspectives of Application

Systematically shrinking copper resources and remarkably declining copper ores grade leads to the growing role of hydrometallurgical processes in manufacturing copper and accompanying metals. Technical, economical, and ecological aspects of application of hydrometallurgy were discussed with regard to dominating smelting methods. Specific conditions of in the Polish copper industry were evaluated and important aspects of necessary application of hydrometallurgy at KGHM for more effective processing of copper ores and concentrates were indicated. The hydrometallurgical unit operations compulsory in unique conditions of Polish copper industry: high content of carbonates, decreasing content of Cu, and increasing content of Pb, As, and organic carbon were analyzed. Hydrometallurgy was recognized as the only real chance for more rational utilization of metal resources from the Polish copper deposits. The advantageous chemical and mineralogical composition of Polish copper ores and concentrates and easy access to sulphuric acid additionally substantiate the need for comprehensive research work.

HPGR comminution for optimization of copper leaching

High-pressure grinding rolls (HPGR) are an accepted, but continuously expanding, comminution technology. The copper industry has a growing need to process harder ores with progressively lower grades, more challenging metallurgy and increasing demand for efficient bacterial leaching applications. This has resulted in a major focus on HPGR use in a crushing circuit. If the industry is to increase leach extraction while lowering energy costs in high-throughput hydrometallurgical operations, HPGR will be of inherent significance. The following paper summarizes test work on copper leach ores utilizing the benefits of HPGR comminution, while increasing several critical metallurgical parameters. Based on the current work and previous investigations, it was found that HPGR comminution within a crushing circuit, in specific instances, can result in 2 - >10% increases in copper extraction. The tested variables are crush size, rock type and copper mineralogy dependence. Various other process parameters may also be optimized.

Preparation of an As(V) solution for scorodite synthesis and a proposal for an integrated As fixation process in a Zn refinery

A method for producing an As(V) solution from an As-bearing material obtained from a nonferrous hydrometallurgical process was investigated. Preparation of the As(V) solution included oxidative leaching of As with a NaOH solution, elimination of As as a calcium arsenate precipitate (johnbaumite: Ca 5(AsO 4) 3(OH)) with a Ca(OH) 2 secondary salt, washing the Ca–As compounds, and reaction of the Ca–As precipitate with H 2SO 4. This process was shown to be industrially applicable. The As ions and Cu ions were effectively separated by oxidative leaching with O 2 gas injection under strongly basic conditions. In this system, As dissolved in the NaOH solution and Cu precipitated with the residue. The dissolved As in this highly concentrated NaOH solution was then effectively precipitated from the solution by addition of a surplus amount of CaO, which allowed recycling of the NaOH solution. The addition of surplus Ca precipitated Ca 5(AsO 4) 3(OH) and Ca(OH) 2, which inhibited the leaching of As but did leach Ca and Na. When the Ca–As compounds were dissolved with H 2SO 4, Ca ions precipitated in the form of gypsum from the As-bearing solution. The gypsum produced by this process is likely to give rise to a number of As-related issues and the As level, therefore, needs to be reduced. This process is advantageous for the treatment of As since it is stabilized as scorodite. The production of an As(V) solution could be applied to hydrometallurgical operations as it necessary for the removal of As. This process is shown to be practically useful to As removal in Zn refining and a closed flow circuit is proposed for integration of this process into a Zn hydrometallurgical operation.

Gold process mineralogy: Objectives, techniques, and applications

The extractive metallurgy of gold is largely driven by mineralogical factors such as gold particle size; association with other minerals; coatings; presence of cyanicides, oxygen consumers, and preg-robbers; presence of refractory gold minerals; and locking of submicroscopic gold in sulfide and sulfarsenide mineral structures. Gold process mineralogy addresses all issues related to gold ore processing by the detailed study of an ore or a mill product. The methodology is widely used as a predictive tool in feasibility studies and during the process development stage, and as a trouble-shooting tool for mineral processing and hydrometallurgical operations.

Ion flotation—its potential for hydrometallurgical operations

Ion flotation is a separation technology for recovering and removing metal ions from dilute aqueous solutions. In this process, an ionic collector is utilized to transport non-surface active colligend ions of the opposite charge from a bulk solution to the solution–vapor interface. If a sufficiently large solution–vapor interfacial area can be provided by sparging gas through the solution, the colligend can be concentrated and removed along with the collector in a foam phase. Ion flotation has a long history for laboratory-scale metal separations, and has been tested at the pilot scale for recovering gold from leach solutions. Although ion flotation has not yet been adopted in commercial hydrometallurgical operations, the process has many attractive features that are promising for treating dilute solutions and effluents. Here, the fundamental characteristics of ion flotation are reviewed in the context of their implications for commercial applications. These characteristics include the kinetics of metal ion removal, the ability to separate target ions selectively from mixed solutions, the ability to manipulate selectivity, the ability to recover metal values from the foam product and a comparison of the performance of ion flotation with widely adopted separation methods such as solvent extraction, ion exchange and precipitation. It is evident from consideration of the kinetics of ion flotation that the equipment traditionally used for ion flotation is far from optimized, and that significant improvements in throughput could be achieved with redesigned equipment.

Electrochemical aspects in some of the hydrometallurgical processes

Hydrometallurgy deals with extraction of metal values from ore minerals through aqueous processing by solubilizing the specific metal value into the aqueous phase and subsequently taking it out of the solution. These steps may be chemical or electrochemical in nature. The electrochemical phenomena depends on the electrical properties of the solid material and the redox characteristics of the solution. The present paper discusses electrochemical aspects of some hydrometallurgical operations involving the following phenomena: (i) corrosion coupling, (ii) galvanic coupling, (iii) dissolution via cyclic action of a redox couple, (iv) displacement or cementation reaction, (v) precipitation under reducing conditions, (vi) dissolution under high pressure, and (vii) dissolution influenced by hole transfer.

Iron oxy-hydroxide crystallization in a hydrometallurgical residue

In some hydrometallurgical operations, the removal of iron from process liquors can be critical, with the method of choice commonly being crystallization (precipitation). It has been recently discovered that if the removal of iron occurs at pH 3, ferrihydrite, a complex and disordered compound, will generally be precipitated. A laboratory scale, computer controlled, continuous crystallizer was constructed to investigate the removal of iron from low pH solutions (precipitation). The significance of ferrihydrite precipitation and the effect of pH and silica concentration on the properties of the precipitate were investigated. Considerable insight has been gained concerning the crystallization and growth mechanisms under these conditions, including the unusual limit of ferrihydrite crystal growth. The use of in situ focussed beam reflectance measurement (FBRM) analysis has allowed the particle size differences experienced at low pH in ferrihydrite precipitation to be studied. The improved understanding of the crystallization of iron from hydrometallurgical process liquors has resulted in a methodology for more effective removal of iron.

The design of bioreactors

A survey of the literature on biohydrometallurgical topics revealed that the papers devoted to bioreactors amount to less than 5% of the total and refer mainly to the analysis of the performance and to design guidelines of stirred tank and of bubble column machines, the so-called Pachuca tanks. These machines can be defined conventional in the sense that they have been borrowed from chemical engineering and hydrometallurgy and adapted to the requirements of biohydrometallurgical processes. However, past experience has shown that these types of reactors do not fully match the very particular conditions that exist in biohydrometallurgical systems that, quite correctly, have been qualified as “hybrid” owing to their specificity since they are characterized by many of the features of hydrometallurgical operations and of biological conversions. Literature data and the author's personal experience demonstrate that one of the present major drawbacks of these reactors is the power requirement that seriously affects the competitiveness of biohydrometallurgy with pyrometallurgy. The factors affecting the performance of biohydrometallurgical reactors are discussed with special reference to the process parameters and an analysis of the conditions to be satisfied by an ideal bioreactor is carried out. In the light of these considerations, the reactors currently operating in commercial plants are examined. The new prospects opened up by recent developments are finally discussed and, also on the grounds of experience recently gained on a laboratory scale, the potentials of machines tailor-designed for the conditions reigning in biohydrometallurgical systems are outlined.

Gas–Liquid Oxygen Mass-transfer; from Fundamentals to Applications in Hydrometallurgical Systems

Oxygen gas is used as a reactant in many hydrometallurgical processes. However, oxygen is sparingly soluble in aqueous electrolyte solutions, and the driving force for its masstransfer from the gas to the aqueous phase is also very low. Hence, the mass-transfer of oxygen depends significantly on the interfacial area between the gas and the liquid phase, which in turn depends on the mixing conditions inside the reactor. A change in the solution composition or the presence of solids can further alter the rate of oxygen masstransfer. All such phenomena related to the gas-liquid oxygen mass-transfer in hydrometallurgical unit operations are critically reviewed in the present article – from the basic thermodynamics and kinetics of oxygen dissolution in aqueous solutions to the most recent advances in oxygen mass-transfer systems.

Gas-Liquid Oxygen Mass-transfer; from Fundamentals to Applications in Hydrometallurgical Systems

Oxygen gas is used as a reactant in many hydrometallurgical processes. However, oxygen is sparingly soluble in aqueous electrolyte solutions, and the driving force for its mass-transfer from the gas to the aqueous phase is also very low. Hence, the mass-transfer of oxygen depends significantly on the interfacial area between the gas and the liquid phase, which in turn depends on the mixing conditions inside the reactor. A change in the solution composition or the presence of solids can further alter the rate of oxygen mass-transfer. All such phenomena related to the gas-liquid oxygen mass-transfer in hydro-metallurgical unit operations are critically reviewed in the present article - from the basic thermodynamics and kinetics of oxygen dissolution in aqueous solutions to the most recent advances in oxygen mass-transfer systems.

Use of technogenic and natural solutions in hydrometallurgical operations

The results obtained here demonstrate the promise of using technogenic and concentrated condensates of hightemperature heat carriers to perform leaching as part of the processing of copper-nickel ores. The productive solutions that were obtained have high contents of the useful components (grams and tens of grams per liter) and could be converted to the desired end products by proven methods [12].

Removal of tin from metal-containing industrial dusts

The separation of tin and other base metals from low-grade metal-containing industrial dusts was investigated using hydrometallurgical operations. Selective leaching of tin could be obtained with oxalic acid solution. Recovery of Sn, Zn, Cu, Pb and Fe from the leach liquor was investigated by solvent extraction with several commercial reagents.

The BATENUS process for recycling mixed battery waste

The first large-scale battery recycling facility implementing the hydrometallurgical BATENUS technology is expected to go into operation by 1996. The plant will be situated in Schönebeck/Sachsen-Anhalt, and has a projected maximum capacity of 7500 tons of spent batteries per year. The engineering is being carried out by Keramchemie GmbH and the plant will be operated by Batterierecycling Schönebeck GmbH. The BATENUS process was developed by Pira GmbH, a research institute in Stühlingen, Germany, during a period of five years. This new process combines hydrometallurgical operations in a nearly closed reagent cycle that involves electrochemical and membrane techniques. Effluent emissions are minimized to the greatest possible extent. Process validity has been proven in a series of pilot plant testings. After mechanical separation of the casing materials like ferrous and nonferrous metals, paper and plastics, the subsequent hydrometallurgical recovery yields zinc, copper, nickel and cadmium. The other products are manganese carbonate and a mixture of manganese oxide with carbon black. Mercury is immobilized by absorption on a selective ion-exchange resin. The BATENUS process is a master process for the hydrometallurgical reclamation of metals from secondary raw materials. It has found its first application in the treatment of spent consumer batteries (i.e., mixtures of zinc-carbon, alkaline manganese, lithium, nickel-cadmium cells, etc.). As a result of its modular process design, the individual steps can be modified easily and adapted to accommodate variations in the contents of the secondary raw materials. Further applications of this highly flexible technology are planned for the future.

Screening tests, in the study of iron oxide leaching by sucrose in sulphuric acid solution, using statistical methods

The dissolution of iron oxide (Fe 2O 3) using sucrose as the reducing substance in sulphuric acid solutions is described. The experimental runs were carried out in homogeneous (reduction of Fe 3+ in solution) and heterogeneous (dissolution of Fe 3+ from iron oxide and its reduction) tests: in the former case, the influence of acid and sucrose concentrations in the reduction of Fe 3+ in solution was studied and several carbon sources were used. In the latter case, the influence of the main factors of dissolution of the iron from the mineral containing the iron oxide was studied; the factors investigated included acid and sucrose concentration, temperature and time of treatment. The results show how the presence of sucrose increases the iron extraction more than two-fold compared with the tests without sugar at the same acid concentration. This makes it possible to carry out a leaching process with a lower acid concentration. Full factorial design was used to plan the experimental work. The results show the potential application of this process in hydrometallurgical operations involving iron oxide dissolution (iron removal from industrial minerals, leaching of iron, etc.).

Recovery of gold from thiourea solutions by flotation

A laboratory investigation was undertaken on the gold-thiourea system over the whole pH range, aiming at the separation of gold by flotation from dilute solutions. Various surfactants were applied, of cationic, anionic and non-ionic type. Among the parameters studied were the initial concentrations of added surfactant and thiourea; emphasis was placed on pH 1.5 (typical in hydrometallurgical operations) and 11. The further addition of ethyl alcohol, acting mainly as a frother, was found to improve gold recoveries remarkably: the recovery reached over 95%.