Show the recovery of zinc bulletin no recovery of zinc from low grade and complex ores by dorsey A lyon and oliver C ralston has just been issued by the bureau of mines department part ment of the interior As is well known to those interested in the metallurgy of zinc volatilization in retorts has been until recently the only commercial process of producing spelter hence zinc mine operators have had to meet the requirements of the zinc smelters shelters sm elters in regard to the following requirements 1 minimum percentage of zinc the ore must contain 2 chemical combination of the zinc in the ore 3 proportion present of those elements that interfere with the successful recovery of the zinc when the ore is retorted due to this fact the bureau of mines station at salt lake city in operation cooperation co with the department of metallurgical research of the university of utah has given considerable study to the possibility of devising new processes for such zinc ores as are at the present time too low grade or too complex to permit of their treatment at a profit by the retort process under normal conditions the low limit of zinc in ores suited to retort smelting smelling is about 25 per cent for oxidized ores consequently the ores or products suited to zinc smelting smelling sm elting in retorts may be obtained from 1 zinc ores free from interfering elements 2 concentrates of zinc ores or of zinc lead ores 3 concentrates cen of mixed and complex ores containing gold silver lead copper zinc etc most of the zinc rec recovered most ot of the zinc recovered from sulphide ores in utah and adjacent states is from mixtures of lead and zinc sulphides sulp hides the usual milling treatment for such ores is to crush size and classify the ores and then separate as clearly as possible the gangue material from the sulphides sulp hides with jigs and tables by this separation of a mixed sulphide ore a lead product and a zinc product are obtained sometimes the lead product contains as much as per cent zinc or even more and the zinc product contains a considerable quantity of lead the zinc that accompanies any lead ore sent to the lead smelter is not recovered therefore the problems connected with the milling of a zinc sulphide ore are as follows 1 14 effecting f a better separation of the lead and zinc materials 2 preventing losses of zinc or of lead and zinc in the tailing treating the ore locally if an ore cannot be rendered marketable by concentration processes the next step is to devise a process for treating the ore locally that is near where the ore is mined so as to do away with the costs connected with transporting the ore and the subsequent smelting smelling sm elting of it in general if an ore cannot be treated at a profit by a smelting smelling sm elting process a process is de the treatment of zinc sulphide ores has been proposed in many different forms during the past half century but has in general failed to be adopted on account of the peculiar chemical properties of zinc and the low value of the products that can be made zinc requires more chemical or electrical energy in comparison with its value after recovery than almost any other major metal on the market and the high consumption of chemicals or of electric energy involved in its recovery has usually made lurg ical processes of questionable value I 1 zinc sulphide resists zinc sulphide resists most ordinary solvents not being dissolved with sufficient rapidity by any of the commercial acids hence requires roasting before the majority of the proposed processes can be applied sulphide of zinc is one of the most refractory sulphides sulp hides to roast and on that account the cost of zinc roasting is higher than that for any other major metal in order to get the zinc into solution after roasting it may be converted into a sulphate or a sulphide or hydrochloric acid may be used as a solvent for the leaching of zinc sulphide ores in lacall localities having industrial plants where acid is a useless product byproduct by hydro acid is also recommended as being a desirable solvent for roasted zinc ores on account of the ease of precipitating zinc from solutions by electrolytic methods however this acid proved to be no better solvent of the zinc oxide resulting from roasting the zinc sulphide than was sulphuric acid or sulphurous acid and its use has no particular advantage as far as leaching is concerned hence experiments with this reagent were discontinued caustic soda has been proposed for f or leaching zinc oxide in many different processes and likewise ammon lacal solutions laboratory tests tests on a laboratory scale were made with all of these reagents As a result of these tests it was found that serious though not insuperable difficulties are to be met in the leaching of most roasted or oxidized zinc ores by either acid or basic solvents as nearly all such ores contain large amounts of acid consuming minerals other than the zinc leaching with sulphuric acid is difficult on account of the tendency of the acid formed to jelly when the solution approaches neutral condition during purification this makes necessary the fuming of the ore with sulphuric acid in order to break up the acid sulphurous acid leaching is also difficult as aa the solutions must be filtered from the ore while acid and hence carry large amounts of impurities also the purification of such solutions is still to be accomplished caus tic soda and solutions do not seem to attack the zinc silicates which are at present in almost every oxidized ore of zinc and precipitation of both solutions promises to be difficult or at least expel expensive problem of precipitation even when the zinc can be put into solution successfully and a high extraction obtained there still remains the problem of precipitation the successful precipitation of solutions containing zinc is the main factor on which hinges the commercial possibility of any process for zinc ores such great purity is required of any zinc compounds usually marketed that chemical precipitation of such a product as zinc oxide in a form commercially acceptable cep table is a difficult matter also when electrolytic precipitation is to be employed manu minute te amounts of impurities are often fatal to good deposition the work reported in this bulletin covers only the concentration of zinc ores and the of zinc the smelting smelling sm elting of zinc ores not being considered investigations were applied to both sulphide and oxidized ores and included concentration tests both by gravity and flotation sulphate and magnetic roasting acid and alkaline leaching and the precipitation of the metal both electrically and chemically tests were also made on the ores to determine their suitability to igneous concentration and magnetic concentration r processes copies of this bulletin may be obtained free of charge by addressing the director of the bureau of mines washington D C |