Zinc recovery from solution

Zinc. The electrowinning of zinc on a commercial scale started in 1915. Most newer faciUties are electrolytic plants. The success of the process results from the abiUty to handle complex ores and to produce, after purification of the electrolyte, high purity zinc cathodes at an acceptable cost. Over the years, there have been only minor changes in the chemistry of the process to improve zinc recovery and solution purification. Improvements have been made in the areas of process instmmentation and control, automation, and prevention of water pollution. 

Pertraction (PT) can be realized through a liquid membrane, but also through a nonporous polymeric membrane that was applied also industrially [10-12]. Apart from various types of SLM and BLM emulsion liquid membranes (ELM) were also widely studied just at the beginning of liquid membrane research. For example, an emulsion of stripping solution in organic phase, stabilized by surfactant, is dispersed in the aqueous feed. The continuous phase of emulsion forms ELM. Emulsion and feed are usually contacted in mixed column or mixer-settlers as in extraction. EML were applied industrially in zinc recovery from waste solution and in several pilot-plant trials [13,14], but the complexity of the process reduced interest in this system. More information on ELM and related processes can be found in refs. [8, 13-16]. 

Zinc Recovery from RFSL Process Solutions... 

Selective extraction of zinc from chloride solutions is required for recovery from primary sources via new sulfide ore leaching technology (Section 9.17.3.3.2) and from secondary sources... 

The zinc concentrate is first roasted in a fluid-bed roaster to convert the zinc sulfide to the oxide and a small amount of sulfate. Normally, roasting is carried out with an excess of oxygen below 1000°C so that comparatively htde cadmium is eliminated from the calcined material in this operation (3). Since the advent of the Imperial Smelting Zinc Furnace, the preliminary roasting processes for zinc and zinc—lead concentrates result in cadmium recovery as precipitates from solution or as cadmium—lead fame, respectively, as shown in Figure 1. 

The classical method of McCoy [133] has been employed for the large scale recovery of Eu from materials containing as low as 0.05% of this element. Reduction of Eu3+ with zinc in HC1 solution followed by coprecipitation of Eu2+ with BaSC>4 is used on industrial scales [134]. 

Cementation, the process by which a metal is reduced from solution by the dissolution of a less-noble metal, has been used for centuries as a means for extraction of metals from solution, and is probably the oldest of the hydrometallurgical processes. It is also known by other terms such as metal displacement or contract reduction, and is widely used in the recovery of metals such as silver, gold, selenium, cadmium, copper and thallium from solution and the purification of solutions such as those used in the electrowinning of zinc. The electrochemical basis for these reactions has been well established414 and, as in leaching reactions, comprises the anodic dissolution of the less-noble metal coupled to the cathodic reduction of the more-noble metal on the surface of the corroding metals. Therefore, in the well-known and commercially exploited44 cementation of copper from sulfate solution by metallic iron, the reactions are... 

The coordination chemistry of both metal ions involved plays a vital role in governing the thermodynamics and the kinetics of such reactions. This will be illustrated by reference to the chemistry involved in the precipitation of gold from cyanide leach liquors by metallic zinc powder — the most widely applied method for the recovery of gold from solutions.415 The overall reaction is... 

Removal of sulfanilic acid from wastewater Lactic acid purification and concentration Enrichment of bisphenol A Phenol recovery from aqueous solutions Zinc(ll) recovery from HCI solution Hydrogen separation from methane steam conversion products... 

The jarosite process separates icon(III) from zinc in acid solution by precipitation of MFe2(0H)g(S0 2 where M is an alkali metal (usuaUy sodium) or ammonium (see Fig. 2) (40,41). Other monovalent and hydronium ions also form jarosites which are found in the precipitate to some degree. Properly seeded, the relatively coarse jarosite can be separated from the zinc-bearing solution efficiently. The reaction is usuaUy carried out at 95 0 by adding ammonia or sodium hydroxide after the pH has been adjusted with calcine and the iron oxidized. The neutral leach residue is leached in hot acid (spent + makeup) with final acidity >20 g/L and essentiaUy aU the zinc, including ferrite, is solubilized. Ammonium jarosite is then precipitated in the presence of the residue or after separating it. If the residue contains appreciable lead or silver, they are first separated to avoid loss to the jarosite waste solids. Minimum use of calcine in jarosite neutralization is required for TnaxiTniiTn recovery of lead and silver as weU as zinc and other metals. 

ABC extractants were found to possess attractive properties with regard to salt extraction. Extraction is efficient and selective. Compared with liquid cation exchangers, ABC extractants are less sensitive to acidity in the aqueous phase and extract alkali and alkaline earth metals better. Both the cation and the anion are extracted therefore, no acid or base addition is required for pH adjustment or for stripping. Extraction is reversible and provides for back-extraction of the extracted salt by water. Several potential applications of ABC extractants in salt extraction were studied, including MgCb recovery from concentrated seawater [2,4,5,7], separation of LiCI [6], removal of Fe from AlCl solutions [14,23], and recovery of ZnSO from zinc electrowinning bleeds [21]. 

Regel M., Sastre A.M., and Szymanowski J., Recovery of zinc(II) from HCl spent pickling solutions by solvent extraction, Environ. Sci. Technol. 35, 630, 2001. 

The copper solvent extraction raffinate is split with a portion of the raffinate returning to leaching and the balance advancing to cobalt, zinc and manganese recovery. The raffinate for cobalt, zinc and manganese recovery is first neutralized to remove iron and aluminum from solution and then subjected to a novel direct solvent extraction process (DSX) developed by CSIRO (Australia) [4-6]. The direct solvent extraction process uses a mixture of Versatic 10... 

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