Separation cadmium

Cadmium may be extracted into CHCI3 or CCI4 as the dithiocarbamate [11,12]. In the presence of tartrate and cyanide at pH 11, only Bi, Pb, and Tl(ni) are co-extracted with cadmium. Dithizone allows a highly selective separation of cadmium. Separation of Cd (and Zn) from Co and Ni has been described [13]. 

HLM process for cadmium separation from wastewaters of the fertilizers industry [71], one of the BOHLM technologies, presented in Chapter 5 in detail. 

Copper-cadmium separation from chloride aqueous solutions [4, 5, 14]. The copper-cadmium separation tests were carried out in a BAHLM module comprising (I) aqueous solutions ofCuCl2 + CdCL, 0.1-0.2 mol/kg each as the feed solutions, (II) an aqueous 0.5 mol/kg PVSNa solution as the liquid membrane (see Table 6.5), and (III) aqueous 0.5—2.0 mol/kg NaCl solutions as the receiving solutions [5]. Cation-exchange membranes Neosepta CM-1 or CMS were used as barriers between the solutions (see Table 6.6). 

Copper-cadiiiitiiH separation in the anionic complex form [5], The BAHLM copper-cadmium separation was tested using (I) an aqueous solution ot Cuds + CdCL, 0.1 mol/kg each, as the feed solution, (II) an aqueous 0.5 mol/kg BPEI solution as the LM, and (III) aqueous 1.0-2.0 mol/kg... 

Only two Marie 22, Mark 16B, Nfork 42 fiiel bundles are allowed b a shipping cask. There are five sections b a cask. Three portions are physically blodoed with blanks 0.e., postions 2,3, and 4) and two are open for fuel storage (i.e., positions 1 and S). One fiid bundle is placed in each section (Ref. 2-2<. Cadmium separator plates are installed b tiiese cask sections to provide neutron absorption capabilities. They are also used to mamtab the barriers between the cask... 

Placement ofthree bundles into two adjacent cask sections. The only mechanism by vdiich bundles could be placed in a critical configuration is by placing them side-by-side without the cadmium separator plates intact... 

SHIPPING CASK WITH BLANKS AND CADMIUM SEPARATOR PLATES... 

The filtered water makeup systems The Disassembly Basin filtration system The MB cutting saw stops The hand-hdd gamma monitors The MB oiticality bars used in the fuel bundling process The HBBS rack spacers and fuel blocking system The shipping cask blanks and cadmium separator plates The installed gamma monitors on the machine basin equipment... 

Cadmium is usually found in zinc ores and is extracted from them along with zinc (p. 416) it may be separated from the zinc by distillation (cadmium is more volatile than zinc. Table 14.2) or by electrolytic deposition. 

Reduction to Gaseous Metal. Volatile metals can be reduced and easily and completely separated from the residue before being condensed to a hquid or a soHd product in a container physically separated from the reduction reactor. Reduction to gaseous metal is possible for 2inc, mercury, cadmium, and the alkah and aLkaline-earth metals, but industrial practice is significant only for 2inc, mercury, magnesium, and calcium. 

Refining Processes. AH the reduction processes yield an impure metal containing some of the minor elements present in the concentrate, eg, cadmium in 2inc, or some elements introduced during the smelting process, eg, carbon in pig iron. These impurities must be removed from the cmde metal in order to meet specifications for use. Refining operations may be classified according to the kind of phases involved in the process, ie, separation of a vapor from a Hquid or soHd, separation of a soHd from a Hquid, or transfer between two Hquid phases. In addition, they may be characterized by whether or not they involve oxidation—reduction reactions. 

Volatilization. In this simplest separation process, the impurity or the base metal is removed as a gas. Lead containing small amounts of zinc is refined by batch vacuum distillation of the zinc. Most of the zinc produced by smelting processes contains lead and cadmium. Cmde zinc is refined by a two-step fractional distillation. In the first column, zinc and cadmium are volatilized from the lead residue, and in the second column cadmium is removed from the zinc (see Zinc and zinc alloys). 

Four different types of junctions can be used to separate the charge carriers in solar cebs (/) a homojunction joins semiconductor materials of the same substance, eg, the homojunction of a p—n sibcon solar ceb separates two oppositely doped layers of sibcon 2) a heterojunction is formed between two dissimbar semiconductor substances, eg, copper sulfide, Cu S, and cadmium sulfide, CdS, in Cu S—CdS solar cebs (J) a Schottky junction is formed when a metal and semiconductor material are joined and (4) in a metal—insulator—semiconductor junction (MIS), a thin insulator layer, generaby less than 0.003-p.m thick, is sandwiched between a metal and semiconductor material. 

Production and Economic Aspects. Thallium is obtained commercially as a by-product in the roasting of zinc, copper, and lead ores. The thallium is collected in the flue dust in the form of oxide or sulfate with other by-product metals, eg, cadmium, indium, germanium, selenium, and tellurium. The thallium content of the flue dust is low and further enrichment steps are required. If the thallium compounds present are soluble, ie, as oxides or sulfates, direct leaching with water or dilute acid separates them from the other insoluble metals. Otherwise, the thallium compound is solubilized with oxidizing roasts, by sulfatization, or by treatment with alkaU. The thallium precipitates from these solutions as thaUium(I) chloride [7791 -12-0]. Electrolysis of the thaUium(I) sulfate [7446-18-6] solution affords thallium metal in high purity (5,6). The sulfate solution must be acidified with sulfuric acid to avoid cathodic separation of zinc and anodic deposition of thaUium(III) oxide [1314-32-5]. The metal deposited on the cathode is removed, kneaded into lumps, and dried. It is then compressed into blocks, melted under hydrogen, and cast into sticks. 

Copper sulfate, in small amounts, activates the zinc dust by forming zinc—copper couples. Arsenic(III) and antimony(TTT) oxides are used to remove cobalt and nickel they activate the zinc and form intermetaUic compounds such as CoAs (49). Antimony is less toxic than arsenic and its hydride, stibine, is less stable than arsine and does not form as readily. Hydrogen, formed in the purification tanks, may give these hydrides and venting and surveillance is mandatory. The reverse antimony procedure gives a good separation of cadmium and cobalt. 

Cadmium and mercury are usually recovered ia separate processes at the ziac plant. The others are shipped as enriched residues to plants that specialize ia their recovery. 

The positive plates are siatered silver on a silver grid and the negative plates are fabricated from a mixture of cadmium oxide powder, silver powder, and a binder pressed onto a silver grid. The main separator is four or five layers of cellophane with one or two layers of woven nylon on the positive plate. The electrolyte is aqeous KOH, 50 wt %. In the aerospace appHcations, the plastic cases were encapsulated in epoxy resins. Most usehil cell sizes have ranged from 3 to 15 A-h, but small (0.1 A-h) and large (300 A-h) sizes have been evaluated. Energy densities of sealed batteries are 26-31 W-h/kg. 

Cadmium occurs primarily as sulfide minerals ia ziac, lead—ziac, and copper—lead—ziac ores. Beneftciation of these minerals, usually by flotation (qv) or heavy-media separation, yields concentrates which are then processed for the recovery of the contained metal values. Cadmium follows the ziac with which it is so closely associated (see Zinc and zinc alloys see also Copper Lead). 

Air pollution problems and labor costs have led to the closing of older pyrometaHurgical plants, and to increased electrolytic production. On a worldwide basis, 77% of total 2inc production in 1985 was by the electrolytic process (4). In electrolytic 2inc plants, the calcined material is dissolved in aqueous sulfuric acid, usually spent electrolyte from the electrolytic cells. Residual soHds are generally separated from the leach solution by decantation and the clarified solution is then treated with 2inc dust to remove cadmium and other impurities. 

In the recovery of cadmium from fumes evolved in the Imperial Smelting process for the treatment of lead—zinc concentrates, cadmium is separated from arsenic using a cation-exchange resin such as Zeocarb 225 or Ambedite 120 (14,15). Cadmium is absorbed on the resin and eluted with a brine solution. The cadmium may then be recovered direcdy by galvanic precipitation. 

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