Electrolytic flowsheet

When the flowsheet is complex and involves numerous process steps, a low-energy efficiency will result. The metals titanium and magnesium are difficult to reduce, and their production involves chloride intermediates which are produced from the oxide raw materials. Titanium requires magnesium or sodium as the reducing agent, and these metals are themselves obtained by electrolytic processes which are energy-intensive. Another feature which may add to the complexity of the process flowsheet is the need to separate impurities and by-products using special processes this is the case with copper, lead, and nickel. 

A major limitation in many flowsheeting systems is the inability to handle electrolytes. New work in this area is now being reported ( 1, 42) and two commercial systems are available (43, 44TT The ASPEN system ( ) has incorporated a solids handling capability to overcome another common deficiency. 

The unit operations in a commercial chlor-alkali plant can be generally classified as follows (1) brine purification, (2) electrolytic cells, (3) H2 and Cl2 collection, and (4) caustic concentration and salt removal. In this section, the general process flowsheets for diaphragm, membrane, and mercury cell technologies are discussed with emphasis on the need for brine purification and the manner in which it is carried out. 

Prior to electrowirniing zinc, all zinc plants must purify the electrolyte, and in particular cobalt has to be removed, usually by cementation with zinc powder. Such a cement can be re-processed to recover its metal values, in particular cobalt. Hydrometal S.A. a subsidiary of Jean Goldschmidt Int. S.A. (JGI) processes such cobalt-containing cements at its plant in Engis, Belgium (31). Cements from various sources are treated, with typical content of 15-20% Cu, 2-5% Ni, 20-30% Zn and 5-7% Co. A simplified process flowsheet is presented in Figure 16. 

Flowsheet for the NALCO (Nalco Chemical Co.) process for the electrolytic production of tetramethyllead (according to [161,163]). 

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