Stage processes extraction Leaching

In the various solvent-extraction circuits employed in this process, use is made of a solution of D2EHPA in kerosene as the extractant. The selective recovery of the various metals is achieved by careful control of the equiUbrium pH value of the aqueous phases in the multistage extraction and stripping operations. After the leach liquor has passed through two separate circuits, each of which comprises five stages of extraction and four of stripping, the europium product is obtained initially as a solution of europium(III) chloride. Further purification of the product is accomplished by reduction with amalgamated zinc to Eu +, which is by far the most stable of the divalent lanthanide ions with respect to the reduction of water cf. the redox potentials of the Eu /Eu and Sm /Sm + couples, which are —0.43 and —1.55 V respectively ). Sulfuric acid is added to the... 

The graphical constmction of the eqnihbrinm stages of solvent extraction can analogously be applied to the process of leaching, as demonstrated in Fig. 6.2-6. 

The British company Reunion Mining Pic (RM) performed a techno-economical feasibility study for the Skorpion mine (Namibia) during 1S 7 and 1998. At that time, RM entered in contact with the R D Division of Tunicas Reunidas S.A. (TR). The objective was to apply the modified ZINCEX process (MZP) to the treatment of Skorpion ore to produce SHG zinc. One of the most important stages of the feasibility study was the piloting of key sections of the process namely, leaching, solvent extraction and electrowinning. 

This part, on applications, covers the following unit operations 8. Evaporation 9. Drying of Process Materials 10. Stage and Continuous Gas-Liquid Separation Processes (humidification, absorption) 11. Vapor-Liquid Separation Processes (distillation) 12. Liquid—Liquid and Fluid-Solid Separation Processes (adsorption, ion exchange, extraction, leaching, crystallization) 13. Membrane Separation Processes (dialysis, gas separation, reverse osmosis, ultrafiltration) 14. Mechanical-Physical Separation Processes (filtration, settling, centrifugal separation, mechanical size reduction). 

Solvent extraction is often used as the next stage after acid leaching. It is based on the addition of an extractant to solve metals so to separate the selected metal. This process has a many advantages such as easy operating condition, low energy consumption and quite good quantity and purity of recovered metals. On the other hand, this process is too expensive for industrial applications. 

Aldehyde linearity is high (ca. 90%). Sufficient N-methyl-pyrrolidone (NMP ca. 40%w) and some water (1 -2%w) are applied to achieve a one-phase system in the reactors. After reaction, water is added in a mixer (phase ratio 1 1 v/v), followed by efficient phase separation in a settler, with virtually all catalyst in the NMP/water layer. The crude product layer is subjected to a multi-stage water extraction to remove residual NMP and catalyst, and a final treatment over a silica-bed to reduce Rh leach levels from 0.2 ppmw to 0.02 ppmw. The recycle catalyst layer (in NMP/water) is dried in two steps, to evaporate water and achieve the low water concentrations required for one-phase reaction, and then recycled to the reactors. Water is recycled, from evaporators, via water extraction, to the mixer. The flexibility of this process with respect to alkene carbon number seems excellent good performance has been found for Cs-C aUcenes [61]. 

The equilibrium stage approach is applicable to other separation processes (absorption, extraction, leaching, etc.) as pointed out in chapter 12. As with distillation, the combination of the mass or material balance, the energy or enthalpy balance, and appropriate equilibrium data will yield the desired design. 

There are two types of extraction processes, namely, leaching where solids are extracted and liquid-liquid extraction. The commonly used leaching equipment is the extraction battery where counter current flow is established resulting in a number of extracting stages. This can be modeled as equilibrium process. The McCabe-Thiele procedure can be used to model this process. In liquid-liquid extraction, ternary diagrams and tie lines are used to determine the extent of extraction. Batch extractive distillation is a commonly used extractive method for liquid-liquid extraction. 

The leaching is normally done using a number of stages. In this respect, the process is similar to liquid-liquid extraction, and the methods used to determine the number of stages required are similar. 

Sulfate process streams are commonly used in metal recovery because they are readily derived by leaching with sulfuric acid or by oxidation of sulfidic ores. Metal recovery from such streams rarely involves the formation of metal sulfate complexes because the sulfate ion is a weak ligand for base metal cations and consequently acidic ion exchange extractants are commonly employed (see Section 9.17.5), which generate sulfuric acid which can be returned to the leaching stage,... 

Extraction is a process whereby a mixture of several substances in the liquid phase is at least partially separated upon addition of a liquid solvent in which the original substances have different solubilities. When some of the original substances are solids, the process is called leaching. In a sense, the role of solvent in extraction is analogous to the role of enthalpy in distillation. The solvent-rich phase is called the extract, and the solvent-poor phase is called the raffinate. A high degree of separation may be achieved with several extraction stages in series, particularly in countercurrent flow. 

The Nippon Mining Co. refinery in Japan, which had previously used D2EHPA to extract cobalt from solutions obtained in the leaching of a mixed cobalt—nickel sulfide in sulfuric acid, changed in 1978 to the new extractant 2-ethylhexyl 2-ethylhexylphosphonate enabling a much-improved selectivity for cobalt over nickel to be obtained.8990 The process is carried out in three counter-current stages with an organic solution of phosphonic acid that has been converted to the ammonium salt by contact with aqueous ammonia ... 

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