42. Create a modern technological scheme of recycling of rare metals from waste of industry

They say that in chemistry there is no useless waste. One proof of the validity of this view of things is the fact that indium is obtained from waste (or intermediates) production of zinc, lead, copper, tin. Used dust fumes, cakes (the so-called solid residues obtained after filtration of solutions). All these substances indium slightly - from thousandths to tenths protsenta.Vpolne of course, that the allocation of such small amounts of item number 49, separating it from the mass of other elements - zinc, cadmium, antimony, copper, arsenic and others - it is very difficult. But "it's worth it": indium is necessary, indium roads.Indium extraction technology, like many other metals, usually consists of two stages: first a concentrate, and then the crude metal. In the first stage separates the indium concentration of zinc, copper and cadmium. This is achieved by simply adjusting the acidity of the solution, or more precisely, the pH value. Cadmium hydroxide is precipitated from aqueous solutions at pH 8, copper and zinc hydroxide - at 6. In order to "land" of indium hydroxide, the pH of the solution should be brought to 4.Hotya processes based on precipitation and filtration, have long been known and are considered well-developed, they do not allow you to extract raw materials from the whole indium. In addition, they require rather cumbersome oborudovaniya.Bolee considered a promising method for solvent extraction.

This process selectively move one or more components of the mixture into a layer of aqueous immiscible organic liquid with it. Unfortunately, in most cases in the "organic" proceeds than one element, but several. Necessary elements extracted and reextracted several times - to transfer an item of water in the solvent from the solvent into water again, from there to another solvent, and so forth, until the complete razdeleniya.Dlya some elements, including indium, found reaktivy- extractants with highly selective. This allows you to increase the concentration of trace elements in the hundreds and thousands of times. The extraction processes are easily automated, it is one of their most important dostoinstv.Iz complex composition sulphate solutions in which indium was much smaller than Zn, Cu, Cd, Fe, As, Sb, Co, Mn, Tl, Ge and Se, indium well, selectively extracted alkylphosphoric acids. Together with indium they pass mainly ferric ions and antimony.

Get rid of the iron is simple: before the extraction solution should be handled in such a way that all the Fe3 + ions were reduced to Fe2 +, and these ions India not companions. Harder with antimony: it is necessary to separate the re-extraction or in the later stages of the production of metallic indium indiya.Metod alkylphosphoric acid solvent extraction (of which turned out to be particularly effective di-2-etilgeksilfosfornoj acid) will significantly reduce the time of receipt of the rare metal, reducing its cost and, most importantly, to extract indium more polno.No so receive only a rough indium. And among the main consumers of element number 49 - the semiconductor equipment (see below); hence, it needs high-purity indium. Therefore roughing refined indium electrochemical or chemical methods.