Show OF LOW GRADE COPPER ORES II by JOSEPH IRVING continued from last issue continuing on spanish low grade ores ore we have ores from the same mines shipped to various countries and treated by an adaptation ap tation of the longmaid henderson and claudet methods the ore is first roasted by the alkali manufacturers for the sake of the sulphur then the cinders which probably contain five per cent sulphur and three per cent copper are mixed with salt ana roasted again by this latter roasting the metals are converted into chlorides which are easily soluble and the fine metals i 1 e gold and silver are recovered by the claudet process the copper being recovered by the usual method of precipitating on iron in this combination method the burnt ore or cinder is ground to eight mesh and during this operation about twelve bergent per cent salt is added and intimately mixed with the burnt ore the whole is then charged into a roasting furnace of th the muffle type A dull red heat is maintained and during the process of roasting hourly samples are taken and tested for solubility of copper in water complete solubility is generally found after about six hours roasting the gases which escape from the muffle furnace are conveyed to a series of condensing towers and the weak acid thus produced is used in the subsequent leaching of the roasted ore the roasted ore is charged while hot into leaching tanks provided with false bottoms of perforated tiles or firebrick covered with a layer of ashes about three inches thick these tanks are ten feet square by four feet deep and will hold about fifteen tons of roasted material the whole charge in the leaching tank gets from eight to ten vash washings ings the first three or four strong washings extract most of the metals the subsequent washings may be used as first washings for another charge As the strong solutions are drained from the leaching tanks they are run first into a large settling tank and a standardized solution of iodide of zinc is added according to the amount of silver in the liquor which has been previously tested the silver and gold are precipitated and when the precipitate settles the clear liquor is drawn off into tanks containing iron and the copper precipitated the iodide of silver and gold As is washed metallic zinc is added and the silver and gold precipitated in the metallic state while iodide of zinc is formed and this latter after being tested is used again on a fresh lot of liquor from the leaching tanks by this method it has been estimated that for twenty cents gold and silver to the value of are recovered from one ton of ore the residue from the leaching tanks known as purple ore or blue billy containing about ten per cent copper and ninety five per cent fes 0 03 is and passed on to the iron foundries it will be seen that there is not much lost or thrown away in the treatment of spanish pyrites forty to forty five per cent sulphur is recovered by the alkali manufacturers in the first stage copper gold and silver are recovered in the second stage and finally grade propositions and the 0 tons which are today lying idle in dumps be made to surrender there values and help hell the commerce of the world ores which contain sufficient pyrites in themselves can be roasted with or without salt and the resulting gases collected and converted into acid with which the metals can be successfully fully leached beached out of the roasted material ores which may have a highly gangue with the addition of th the e RESULTS OF ROASTING VARIOUS ORES WITH PROPER AMOUNT OF no of weight of amount of copper insoluble in extraction test charge pounds water per cent 1 at start after four hours after six hours after nine hours 0 7 ad after eleven hours after twelve hours boo 2 at start after seven hours after ten hours 82 3 at start after six hours after nine hours 4 1500 at start 1140 after one hour af after ter seven hours after nine hours af after ter eleven hours af after ter thirteen hours after fifteen hours 97 5 2000 at start atter after three hours after five hours atter after nine hours after twelve hours no pyrite used the iron goes to the iron and steel manufacturers rs it is quite possible that the out door method as practiced in the south of spain may not appeal to the present day idea of making money fast or again the vast majority of the low grade ores of the western states may not admit of treatment on the henderson claudet lines still there is surely some happy medium that might be carried out with good effect on these row ne necessary essary amount of iron pyrites which i and t tl itself may carry some values further addition of salt can be roasted i from six to twelve hours and the coppi coppe gold and silver leached beached out by means water and dilute acid the latter being 0 ote bained as a product byproduct by from the roast tb latter is practically a ineth and has been carried out by the author australian ores and on mixtures of ores a and 0 ol 01 tailings which contained from two half per cent to four per cent copper and a little silver the silver was recovered with the copper these tests were carried out in a small furnace of the muffle type and during the operation of roasting samples were taken and tested for solubility of copper see tests 13 1 3 further experiment proved test 4 that not only on low grade ores was this chloria ising treatment profitable but that high grade material was also amenable and on commercial lines it should be noted here that these ores were highly running from sixty per cent to seventy per cent silicia and from ten per cent to fourteen per cent the roasted material was washed with water and dilute acid from condensing tower and the resulting liquors precipitated on iron the precipitate obtained gave seventy per cent copper and thirty ounces per ton in silver the original ore averaged about three ounces per ton in silver crushing was rather an important factor as material crushed only to 4 mesh took much longer to roast and presented other difficulties while mixtures which were crushed to 16 mesh were acted upon very quickly and thoroughly many more tests were carried out on the same lines the proportion of salt and pyrites varying from five per cent to twelve per cent some further tests were carried out on the same lines but without adding iron pyrites to the mixture salt only being used test 5 more time was necessary and a greater proportion of salt was required one may say that a six per cent copper ore should be smelted smelt ed but an ore with seventy per cent silica and fourteen per cent aluminum takes quite a lot of fluxing flexing flu xing which it is not always easy to get hence it is necessary at times to try other methods the results obtained on these australian ores encouraged the writer to try a similar method on some ores from utah and nevada the material from utah was very low grade running only per cent copper roasted with salt an extraction of per cent was obtained residue tails going per cent the ore from nevada gave per cen cent copper ounces silver ounce sold gold roasted with salt an extraction of per cent was obtained tails going per cent copper ounce silver trace gold the ores most amenable to the foregoing treatment i e preliminary roasting or are those which contain a fair amount of sulphide present either as iron pyrites or as Is often the case containing a mixture of both A careful analysis of the ore will determine whether it is better to give it simply a sweet or sulpha roast or a chlo rid izing roast the cost of salt will do all that is wanted and the fumes evolved and condensed will produce sufficient acid to give the proper leaching effect it must always be remembered in connection with either roasting to sulphates or that there is always the extra cost of furnace installation to be considered also towers for condensing the fumes from the furnaces and producing the necessary acid naturally there is no need to buy acid and the solvent is always to hand and in quantity to be continued |