Show effia efficiency ency of acl acid d 1 in n copper leacha Le achini ng by OLIVER OLIVE R C BALSTON AND D A LYON the question as to how much acid should be bd expected to do useful work in copper leaching and how much can toe be lost is ont one that has become of some moment during the past few years some isome have labored under the impression that a certain amount of acid can be put onto an ore the copper dissolved and all the acid recovered by depositing the copper however when it is found that from 20 to so 80 per cent of the acid applied does useless work is dissolving iron aluminum lime etc the conclusion may be jumped at that such an ore is not adapted to a cyclic process where acid may be recovered as only the acid combining with the copper is recovered by electrolysis it may also discourage one from attempting a further investigation of the maiter when trying to extract copper with only the theoretical amount of acid for dissolving the copper of the ore to find that he obtained only a low percentage of extraction generally to his surprise one learns that thai he must use two three or even five times as much acid as that which will theoretically convert the copper in the ore to copper sulphate or copper chloride as the case may be after looking over the accompanying table of acid efficiencies one is inclined to look askance at the regenerative acid schemes without number which have lueen proposed in recent years to be sure for every pound of copper deposited an equivalent of acid is regenerated but taking tile the losses of 75 per cent of the acid at the from department of metallurgical ficai research university of utah russia mine for example the other 25 per cent which could be regenerated is rather small the accompanying table gives the acid efficiencies of several plants which have been in operation for some time as well as the tests which have caused several companies to decide to build plants for extracting copper from its ores this data has been gathered from the literature where the acid efficiency is usually reported in ill pounds of acid used up on the ore per pound of copper dissolved this means actual pounds of without taking into account the water always found in commercial sulphuric acid thus 66 degrees beaume sulphuric acid is only 93 per cent 4 1 H cosoi by weight if the copper minerals wera were the only ones attacked by acids one pound of copper would require about 1 15 55 lb ib wherever the consumption of acid on an ore is higher than this figure the excess over is reacting on some soine other constituent of the ore and is being lost for example the figure of the arl arizona copper co giving 2616 lbs ibs 1120 dissolved used up per pound of copper shows that 2616 equals 1066 lbs ibs are 1 being wasted the efficiency of the acid aci is hence divided by 2616 or V per cent therefore the table shows acid CORI con expressed in pounds of acid per P pound of metal extracted acid efficiency of the t g by which is meant the percentage and the acid which is usefully expended a so percentage extraction of copper is ob appended lor for completeness wherever I 1 tai the costs of the acid used ILSO in all cases are given f the rather recent data of croasdale are given at some length showing the lab I 1 oratory and large scale tests which made the calumet and arizona copper company decide on building a large leaching plant in ajo the data obtained by the shannon copper company which made them decide not to leach their ore is also given for more complete details the original articles can be consulted the point to be brought out however is that plants have operated for years on small amounts of copper and with losses of acid never smaller than 40 per cent and even as high as 75 per cent of the acid applied |