Show estimating gold silver platinum 0 num in material high in copper BY C V V DAVIS two general schemes have been used for the determination of gold and silver in material containing considerable quantities of copper one is known as the all fire method and the other as the combination or wet and dry method the all fire crucible method using an excess charge of has been found satisfactory when the copper content of an ore is under 6 per cent loevy J vur in Kupfer enzen chem zag Jarli jarling rg 35 1911 p or where the precious metal value is so great that a small sample can be used in the latter case silica is added until the copper ratio is sufficiently low if there is more than 6 per cent of copper in an ore the lead button obtained from a crucible will require repeated before it can be cupel led successfully cess fully Re is not only tedious but also causes a slag loss of precious metals in combination methods the copper is dissolved and the gold and silver in the residue is determined by fire assay although some combination methods have given satisfactory is results for gold and silver they are not applicable when an estimation of the platinum metals is required since substances containing platinum are frequently high in copper a study of methods which might be used for the estimation of small quantities of gold silver and the platinum metals in such material was considered worth while the estimation of platinum in ores by fire assay methods has been described in technical paper of the bureau davis C W the detection and estimation of platinum in ores U S bureau of mines tech paper 1921 the present paper which is supplementary tary to that report deals chiefly with the application of combination methods taking them up to the point where the fire assay is to be applied methods for oxidized ores the treatment described below for oxidized copper ores is based on the fact that the copper in such material is soluble in dilute sulphuric acid whereas silver gold and the platinum metals are not as a rule attacked by that reagent A representative sample consisting of an assay ton of the finely pulverized ore is heated in a beaker with c c of sulphuric acid 1 I 1 part concentrated sulphuric acid to 10 parts of water the hot digestion should be completed in about fifteen minutes then enough sodium chloride is added to precipitate any silver that might be in solution and after stirring for a min Assil stant chemist bureau of mines ute or two five drops of a 10 per cent solution of potassium iodide are added to precipitate palladium the solution is heated to boiling and then about 10 c c of saturated lead acetate solution is introduced to aid the settling of finely divided metals and compounds the potassium iodide will precipitate all the palladium and also carry down an insignificant amount of copper A large excess of potassium iodide however will palladium although the silver and palladium are usually in an insoluble condition so that the addition of pre may not be necessary it is best to be on the safe side and add sodium chloride and potassium iodide after standing until clear preferably over night the copper solution is decanted through a filter paper and washed with hot water care bare should be taken to keep the solution sufficiently dilute to prevent crystallization liza tion of copper sulphate on the filter paper for this would stretch the pores of the paper and let fine particles go through through the filter the residue is extracted with fresh portions of sulp sulphuric hurl c aci acid d in order to dissolve additional copper and the filtrates produces tro duces an unnecessary chance for mechanical ch anical loss of material if only gold and silver are sought ordinary fire assay methods may be used but if the platinum metals are required special methods which are described in technical paper should be used the accompanying table shows that with careful manipulation results may be obtained by a combination process that check closely those secured by all fire methods comparison of results samples were ground to pass a mesh screen and thoroughly mixed mg of palladium was added to each of samples 1 2 3 4 9 10 11 and 12 and 1500 mg of silver was added to each of the other check assays essays were run and the results corrected for losses method for sulphide ores the combination methods generally used for the determination of gold and silver in copper sulphide ores are not satisfactory when the platinum metals are to be estimated for methods such as that of van liew van liew R W losses in the determination of gold and silver in copper bullion their causes and a method for overcoming them eng and ming jour vol 69 1900 p using nitric acid would dissolve palladium if it were present A number of experiments were conducted in order to find a solvent which would remove the copper from copper sulphide sulp bide ores kam alg ale deseria 11 1 method ir tl all AH inre method no tion of ore per p er cent ag aff nig m g au mg pd ing in g pt mg ing aging ag ing mg au ing I 1 pd mg pt rag mg 1 carbonate 2 11 3 11 4 11 7 0 42 5 72 1815 OAS 6 57 1826 62 6 72 ISIS 7 i 72 1842 1831 8 72 17 1852 0 62 9 sulphide 1541 1562 10 1548 1543 11 1512 1562 1502 12 1 1198 the sanT samples ples of ore anal analyzed seel zed were kindly donated jy by W S palmer prof professor assor of metallurgy argy at the university of nevada treated as before to save dissolved silver it is not necessary to remove all of the copper but its content in the residue should not be large when sufficient copper hae hac been removed the residue is transferred to the filter paper care being taken to remove any particles that may stick to the beaker this is best done by using a rubber rubber policeman and a stream of hot water one assay ton of is put into a fire clay crucible and the moist filter paper with its contents are placed on oil top of the charge at first the material is heated slowly then the temperature is raised until the filter paper ignites the crucible is then covered removed from the furnace and cooled the material is then ready to be mixed with suitable fluxes and analyzed by fire assay methods the moist residue and filter paper may be heated in a roasting dish but this procedure in without attacking the precious metals the th most promising reagent tried was a mixture of ten parts of 3 per cent hydrogen peroxide and one part of sulphuric acid specific grav grat ity by volume with this mixture the th copper from some sulphide ores was dissolve bid hidi ed in a few hours while the copper sulp of other ores was only partly decon decompose decomposed POsed I 1 by long continued digestion I 1 in order to convert a sulphide ore to v form in which the copper would be in dilute sulphuric acid a preliminary roast 4 boffl 00 1 was used loss of silver occurs when sulphide ores are roasted at a tempera temperate tempe ratu tur sufficiently high to break up sulphates tta abal of fir 4 are formed fulton C H A manual assaying 2nd and ed 1911 p but SO sia itis desirable to have sulphates present best temperature to use will cause no voa utilization losses of the precious metals i one assay ton of a satisfactory samp ore is placed in a roasting dish of such size that the material may be stirred without danger of spilling the material is carefully roasted with occasional st stirring arri ng the temperature pera ture should be low at first and gradually t increased until at the end a dull red heat is maintained but it should not exceed deg t C at any time the stirring should be care fully done in order to prevent loss a bent iron wire being convenient for this purpose f if the material decrepitates decrepit ates it should be covered by an inverted roasting dish until all danger of loss is over if the ore becomes fused by too rapid heating a new sample should be used and greater care taken in its roasting when the odor of sul dioxide can no longer be detected the ore is cooled and then treated exactly as in the method given for oxidized ores this procedure will give accurate results only when the is willing to use care le in his manipulation and is free to give necessary attention to the details of the pron 3 icess A few results of the assay of sulphide s tores ores are given in the table T S d s method for bullion 3 31 combination methods for copper bullion or matte involve the use of either nitric acid van liew work cited or concentrated di sulphuric acid hunt F F determination of gold in copper bullion eng and min jour vol 87 1909 p alone or both of these acids in combination with cupric suli 3 phate mercuric sulphate or mercuric nitrate flinn P F B assay of gold old in copper bul lion eng and min jour vol 87 1909 p these reagents dissolve palladium which anc once e dissolved in a nitric acid tion together with large amounts of copper ai is i difficult to recover 64 56 in order gordej to get around this difficulty a 55 solvent was sought which would dissolve me allic copper without affecting finely divided platinum metals after many failures it was found that a mixture consisting of one part 0 of f concentrated sulphuric acid and ten parts I 1 pt t f 3 per cent hydrogen peroxide would ac II 11 rr this when the metals were present chur agether og ether when the metals were alloyed ja id ith copper however palladium went into gr gj y solution along with the copper but was pre tl imitated by means of potassium iodide after goli boiling off most of the hydrogen lerox P de and then decomposing the rest with fer PO pus ous sulphate I 1 A sample of copper bullion as finely dito aided as convenient good samples are ob 1 I ined by sawing small bars or ingots ingols of ra etal and d using the sawdust is treated with 0 goal mixture of ten parts of 3 per cent hydrogen ratu atu oxide roxine and one part of concentrated t auric uric acid about c c of the mixture yc of f 3 required for an assay ton of metal after si git is nearly complete the material is at oiled for about half an hour to remove most ya r the hydrogen peroxide and ferrous sul hate is added to comple complete te the reduction hen len sodium turn the ale chloride is added and pro r api P cedore given in the method for oxidized ores is followed when the metal is not readily attacked by the previous treatment the copper may be dissolved in nitric acid together with silver palladium and other metals and the solution evaporated to dryness the residue being heated and finally extracted with dilute sulphuric acid to remove the copper concentrated nitric acid is gradually added to a sample of copper bullion contained in a covered beaker until the material is completely decomposed every three grams of copper require about 14 c c of nitric acid specific gravity the acid is best added by means of a pipette whose tip is introduced between the watch glass cover and the lip of the beaker the solution is then evaporated to dryness on a steam bath or hotplate hot bot plate and the beaker is placed on a wire gauze and heated at deg or higher until no more fumes are vis ible the correct temperature can be obtained by having the gauze under the beaker at red heat the residue is then mixed with a glass rod and the heating continued for half an hour the copper is now oxidized and all nitrates that were formed have been decomposed by the heat although osmium that may have been present will have been changed to the and volatilized its loss would occur anyway in the fire assay the roasted material is extracted with warm dilute sulphuric acid and the procedure followed that was given for oxidized ores copper bullion may also be decomposed by heating with concentrated sulphuric acid or by fusing with ammonium sulphate roasting and then extracting with dilute sulphuric acid but the evaporation of sulphuric acid is tedious and the fusion requires a large excess of flux to convert all the copper to a soluble form |