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Cyanide processes for the'recovery of precious metal values from ores commonly employ an alkali-cyanide solution which is contacted with the crushed ore solids to dissolve the gold and/or silver as a complex metal cyanide. The solution is then separated from the ore solids,<a href="http://www.lightcrusher.com/solutions/mobile-crusher-for-sale.html">mobile crusher for sale</a> and is clarified and contacted with a precipitant which in the more modern plants is zinc dust. The mixture of solution and zinc dust is passed through a suitable collecting filter for removing the precipitated concentrate. The efiiciency of precipitation is improved by deaerating the solution prior to precipitation. Throughout the process the cyanide solution is maintained in alkaline condition in order to prevent loss of cyanide.In conventional practice relatively large volumes of cyanide solution must be precipitated, it is not unusual to have to precipitate from 2 to 3 tons, and in some cases as high as 4 or 5 tons, of solution per ton of ore solids treated. Because of the attendant cost, and large capacity equipment involved, a process for the recovery of precious metal values which would entail precipitation of relatively small quantities of solution per ton of solids treated would provide appreciable econo mies in operating costs and equipment required.
The operation of separating the enriched cyanide solution from the ore solids constitutes a' substantial item of cost in conventional cyanide; processes, as well as requiring the installation of comparatively expensive plant equipment to carry it out. Furthermore,<a href="http://www.lightcrusher.com/solutions/silica-sand-mining.html">silica sand mining</a> ore slimes are frequently of such a nature that separation or removal of the enriched solution is extremely diflicult and is often attended by appreciable losses of'dissolved values. In other cases thevalue of the material to be treated, as for example tailings from former operations, is not suificientto warrant the installation of the relatively expensive apparatus required to separate the solution from the waste ore solids or to bear the operating costs of this step and hence cannot be economically treated by'conventional practice. h
It is therefore desirable generally to'be able to recover the dissolved values" from such ore pulps and low grade material without" the" step or s parating from Y the ore solids the alkalianid sol t e tai i sthe d s o v va ues.- W as e n rd o. Sofia di 's l ed me als fro cid "or neutral solutions of the same by the riser?- 1 1 1-"e c ange resins; Thus the prior art teaches-that. polyamin'e anion exchange resins in the exhausted or salt condition will s'orb dissclvimeta ls such as gold from acidic or neutral somtio s n; which the metal exists aisa complexja'cid anion such as the jchloroaurate anion. Prior art see Industrial and Engineering chemistry; Vol.37, p. 6 18, July 1945) teaches further t liat sorption involving metal acid com- 1316); anions does not occur in any appreciable amount with a polyamine anion'exchanger in the" free base 'conditi on, that is an exchanger base unjless "the solution containing the complex metal anion is acidic, andprior art also teaches that alkaline solutions desorb or remove'the sorbed metal from anion 'eiichangers.