The geochemistry and mineralogy of REE deposits is diverse, from carbonatite-related deposits, alkaline rocks, mineral sands and ion adsorption clays to potential by-products of phosphate and bauxite, and reuse of waste materials. Despite the large number of prospects that have been explored recently, very little additional REE production has started. A major challenge is to design effective, cost-efficient and environmentally-friendly processing and extraction. Processing flow sheets have to be constructed carefully for each deposit. Translating geochemistry and mineralogy studies, including quantitative mineralogy results, into processing characteristics can be illustrated using results from the Songwe Hill carbonatite, Malawi. Combining results with other published data then allows us to make some general conclusions about the common REE ore minerals and their geological environment, including the REE fluorcarbonate series, monazite and xenotime. The use of chemicals for REE extraction is often the largest environmental burden to mitigate. A new issue is that certain REE, such as Ce, are in oversupply, and are not being recovered in some proposed processing flowsheets. It will be important to understand the environmental and commercial implications of this development.

The geochemistry and mineralogy of REE deposits is diverse, from carbonatite-related deposits, alkaline rocks, mineral sands and ion adsorption clays to potential by-products of phosphate and bauxite, and reuse of waste materials. Despite the large number of prospects that have been explored recently, very little additional REE production has started. A major challenge is to design effective, cost-efficient and environmentally-friendly processing and extraction. Processing flow sheets have to be constructed carefully for each deposit. Translating geochemistry and mineralogy studies, including quantitative mineralogy results, into processing characteristics can be illustrated using results from the Songwe Hill carbonatite, Malawi. Combining results with other published data then allows us to make some general conclusions about the common REE ore minerals and their geological environment, including the REE fluorcarbonate series, monazite and xenotime. The use of chemicals for REE extraction is often the largest environmental burden to mitigate. A new issue is that certain REE, such as Ce, are in oversupply, and are not being recovered in some proposed processing flowsheets. It will be important to understand the environmental and commercial implications of this development.

This paper, which is the second in a series of three, follows a previous study that showed that Light Rare Earth Elements (LREE), hosted in monazite and rare-metals (Sn, Nb, W), hosted in cassiterite, rutile and wolframite, respectively, are pre-concentrated in the micaceous residue of a kaolin plant. However, the low grade and fine size range of the metal-bearing minerals make their recovery difficult using unique gravity concentration methods. An enhanced gravity concentration flowsheet was tested, which began by screening the residue into three size fractions: +180 mu m, 180-53 mu m and 53 mu m. The 180-53 mu m fraction was treated with a spiral as a roughing unit and then a shaking table as a cleaning unit, whereas the fine 53 gm processing is addressed in the third publication. The design of experiments (DOE) methodology was used to set the best operating parameters. The best heavy mineral recoveries for the spiral concentrate were obtained at a low wash water flow rate and low pulp density. The spiral scavenging tests showed that up to 80% of the heavy minerals can be recovered. However, the mineralogical analysis showed that after three passes, middlings began to be recovered, suggesting that the scavenging operations should not be further continued. Furthermore, up to 70% monazite could be recovered in a single pass. Shaking table testing on the spiral concentrates showed that heavy mineral concentrates with up to 98.5% of heavy minerals can be recovered. However, the concentrate grades were still low for most metals (Sn, Nb and W), with the exception of LREEs, which reached up to 1.6% LREE in the shaking table concentrate. Given the reasonable overall recoveries, the main reason for the low concentrate grades could have been the very low.grade of the feed material, which was two to three times less enriched in metals than the average micaceous residues grades. This suggests that the cut-off grade for those metals should be above 100 ppm and points to the critical aspect of metal grade variability in the micaceous residue as a major issue if potential industrial applications are to be considered. (C) 2016 Elsevier Ltd. All rights reserved.

Energy intensive classical metallurgical processes, the depletion of high-grade ores and primary sources push the scientific and technical communities to treat lean and complex ores as well as secondary metal resources for the recovery of valuable metals. Chlorination technique could be a suitable technology for this purpose. This paper Summarizes laboratory experimentation of chlorination processes developed for the extraction of tantalum and niobium from their bearing materials, the upgrading of chromite, the treatment of sulfide concentrates, and the decontamination of jarosite, as well as for the synthesis of potassium ferrate.Each investigation started by a thermodynamic study of different systems (M-O-Cl, M-S-Cl, M = metal) including the calculations of the standard free energy of chlorination reactions and phase stability diagrams of these systems. The kinetics of these chlorination reactions was studied by thermogravimetric analysis. The effects of total gas flow rate, temperature, individual reactant partial pressures, etc., on the chlorination reaction rate were investigated. Besides, experiments were also conducted in tubular furnaces. Several different qualitative and quantitative analyses methods were used to evaluate the selectivity and performance of the chlorination processes.The results reported in this paper show the advantages of the chlorination technology in terms of energy saving. selectivity of the processes,and recovery rate of valuable metals. They also demonstrate the possibility to treat lean raw materials, to improve the decontamination of wastes, to generate environmentally safer residues, to engineer new compounds, etc. (C) 2009 Elsevier B.V. All rights reserved.

Understanding the formation and the destruction of large organometallic aggregates obtained by precipitation first requires a description, at each step of the precipitate evolution, of the mode of filling space by aggregates. This evolution results (for example, in a precipitate flotation) in opposite processes of packing and breaking; thus, the description needs to be precise in time and space. Unless there are proofs of 3D anisotropy, the description is made in two dimensions so that it consists in the geometric characterization of a plane-closed boundary. The planar description leads to two series of parameters: micromorphologic and macromorphologic, both being computed from a standard descriptor, which is the polygonal finest vector chain called Freeman chain. The first series intend to find some possible scaling process on the whole boundary or only on sampled arcs characterized by fractal invariants. The scaling laws thus yielded can be stated “fractal” only over a limited scale range included in the size interval between the body size and the resolution threshold of the measurement device. This invariant was studied on organometallic molybdenum aggregates. An analysis of the particle morphology puts in evidence at least two populations of flocs in the Mo precipitate in addition to the genuine germs whose structure is regular. The fractal dimension variations prove the structure heterogeneity of the aggregates. Large flocs with Df in the interval from 1.20 to 1.25 are formed either with more compact microflocs (Df=1.10–1.15) or with regular elementary germs (Df=1.02–1.05). The coincidence between morphologic features and physicochemical properties is obvious and interesting.

Neves-Corvo mine (SOMINCOR, Portugal) is one of the most important underground mines now operating in Europe. It treats a heterogeneous massive sulphide deposit, which is mainly copper and/or tin rich. The extracted ore is processed to obtain two types of concentrates (Cu and Tin) whose purity is affected by some minor (As and Sb) and trace (Hg, Se, Cd) elements. In addition to the concentrate sales, silver is also commercialized as a bonus product. The present work intends to identify the mineral bearer of some of these additional detrimental or bonus elements, and to develop a mineralogical model for predicting mineral processing production profits. Many laboratory-scale tests were conducted to study the behavior of minerals: the different steps and conditions of these tests allow good reproduction of the industrial flotation process of the Neves-Corvo mine. The statistical analyses of the elemental distributions give interesting results and provide the ingredients from which we can produce a preliminary predicting tool. Thus, fahlores-minerals (tetrahedrite and tennantite), which are considered to be veritable toxic trash minerals, can be easily localized during the process. This will allow their separation by modifying the flow sheet to improve the concentrate quality.

The limiting factor for metal-organic precipitate flotation in a column is the level of aggregate stability under the turbulence created by the rising bubbles. The hydrodynamic conditions in a 75 mm diameter pilot column were optimised by using different bubble spargers (Microcel, Flotaire, Imox) and by varying the gas flow rate into the bubble sparger, feed flow rate in the column, type and concentration of frother and recirculating pump flow rate. With the bubble spargers used, the average bubble diameter ranges from 0.30 and 1.10 mm, with up to 25% gas hold-up. The parameters influencing average bubble diameter are the superficial gas velocity and the recirculating pump flow rate. For optimal concentrations (10 to 20 mg/1), the type of frother has a negligible role.

Most of the naturally occurring iron, titanium and chromium bearing minerals which accompany industrial minerals, such as quartz, feldspar, nepheline syenite, spodumene, andalusite, vermiculite, etc., exhibit either ferromagnetic or paramagnetic properties and can therefore be removed by means of magnetic treatment.

The influence of the particles shape of crushed and floated talc for different size fractions on the whiteness index (parameter Y) was quantified by the fractal dimensions D-f of the contour roughness and D-g of the size distribution. Contours were obtained by an image analysis method and the fractal dimension D-f was calculated by the Richardson-Mandelbrot method. Frequency distributions of D-f for the talc particles < 20 mu m show higher values of D-f (between 1.25 and 1.35) after wet grinding in a ball mill with ceramic grinding media (Y = 85-86%) than after dry grinding with hammer mill Forplex (Y = 88.5%). This can be related to an increase of the number of particles with complex morphology that could influence the light distribution during the whiteness measurements. An increase in D-g values can be related to the presence of greater number of fine particles that could influence the quality of floated concentrates and then correlatively the whiteness of this concentrate.

In addition to problems inherent to flotation of precipitate or element of negligible mass, ion flotation of Cr6+ is particularly difficult as the same chemical plays both the role of precipitating, dispersing; and frothing agent. A major consequence of this situation involves nearly impossible precipitate adsorption on bubbles and carrying away of particularly stable and loaded froths with the liquid. Flotation columns are tools well-adapted to the collection of precipitate because of the weak energy dissipated during flotation. Besides, several modes of association of bubble generator/column have been tested and it has thus been possible to develop a new mode of precipitation-flotation called ‘Precipitation on bubbles’. With this new mode, the rate of Cr6+ removed by column flotation is about 81% for a collector/Cr ratio of 1.2 and with between 1 and 4% liquid lost in the, froth. A re-treatment of the exhausted solution allows to obtain a total Cr recovery of 91.6%.

Ion flotation of molybdenum in sulfuric acid leach solutions of uranium was performed using a flotation column (75 mm diameter, 3 m height). Three bubble generators (Microcel, Flotaire and Imox) were tested to achieve the flotation of the precipitate formed between Mo and alpha-benzoine oxime. The studied parameters were bubble diameter, energy dissipation and initial Mo concentration. From the lab and pilot plant results (>95% Mo recovery), was estimated the possibility of determining the number of flotation column which would be needed for purification of solution coming from three industrial plants.

As a result of the numerous studies carried out on assorted phosphate deposits by various methods, a new technique has been developed in the laboratory for the differential flotation of phosphates, especially sedimentary ones, with the aid of collectors which are amphoteric, i.e. they simultaneously possess a cationic and an anionic function, according to the working pH.