Show CYANIDE PROCESS the following 11 very able paper on the development of the cyanide process was read by wm win orr M E and western representative of the gold and silver extraction company of america at the international dl mining dono congress 1 re ss hold held in this city last summer mr president ladies and gentlemen the object of this paper is to draw your attention to the development of the cyanide process within the last five years and the great benefit the mining industry has derived five years ago ago the total cyanide mills in america would not exceed five or six six 1 in in number and today I 1 am conservative in in stating that there are aver over fifty plants in the united states employing the mcarthur for est cyanide process take the state of utah for example in 1895 there was only one cyanide mill in operation namely th the famous old mercur mill with the history of which nearly everyone is familiar and today there are in operation or in course of erection no fewer than fifteen cyanide plants within the boundaries of the state in camp floyd commonly called mercur district alone there are ten cyanide plants and as this district is is dependent entirely on the cyanide process for its ore reduction I 1 will give you a brief sketch of the methods which have been employed and the difficulties which 1 I as the representative of the macarthur forest co have encountered in the reduction of the ores of this district by means of cyanide the ore is principally an altered or limestone which can be easily pulverized in fact this feature of the ore was the cause of the first difficulty encountered by the pioneer operators fine crus crushing hinr was entirely out of the question for this ore as the fineness thereby produced entirely stopped the circulation of the cyanide solution here the extremely porous character of the ore came to the assistance of the millman enabling 6 him to leach the ore in a coarse condition from a 1 I 1 4 to I 1 mesh when he would otherwise have been driven to employ agitation and decantation as his method of extraction instead of the simple and economical method of percolation beginning 1 by crushing the ore to 10 mesh which was found impracticable the mesh has gradually been raised until i 4 1 1 mesh has been reached in some cases from i to i P mesh however has been found to yield the best results but here it is difficult to fix a definite mesh for all the mines in the district as they vary considerable in character some such as the geyser marion and brickyard being much more in character than the mercur Ker cur sacramento or sunshine four or five years ago it was considered necessary to leach the ore at least four days but this was 11 eventually found unnecessary and the time has been reduced to from forty eight to seventy two hours and may in some cases reach eight eighty y four hours with talcy dalcy ores it is a remarkable fact that the gold in the ore in this district can be entirely brought into solution in fifteen minutes under favorable conditions such as bv ao agitation at 10 mesh so that on a commercial scale the time taken in obtaining a satisfactory extraction is chiefly required in actually washing out or displacing the first solution which from experiments peri ments I 1 have made I 1 conclude must have dissolved the greater part of the gold the strem strength th of the cyanide solution employed has also been greatly reduced and now the strength 11 generally used varies froin framl 1 lo 10 to 2 10 of 1 per er cent and I 1 have seen a solution containing 1100 1 of 1 per cent produce an excellent extraction but the precipitation with this solution was imperfect until the solution was re strengthened the result of this change chance inthe in the strength of the cyanide solution now employed from that used five years acro ago 11 namely i of 1 per cent to 1 per cent is a great reduction in the loss of c cyanide y anide and therefore in cost A great saving in the loss of cyanide in some cases has also been effected b by Y the addition of lime thereby neutralizing the acid salts deleterious to the cyanide and which occur principally in surface ores in fact on one occasion occasion I 1 experienced the total loss of the cyanide in solution and on investigation found it was due to the presence of some surface surf ace ore from a new ore chute the ore from which contained a large amount of acid salts on testino testing 11 this ore I 1 found the loss of cyanide without the addition of lime was 9 pounds per ton with lime added I 1 of a pound per ton without careful attention an occurrence of this kind will result in a heavy loss of gold in the tailings if the trouble is not speedily located and overcome the acidity in the mercur oxidized ore is principally due to acid iron aluminum and magnesium salts which can be neutralized to a large extent by the use of lime this lime is is added as the ore is charged into the tank the quantity used being r from one to two pounds lime per ton of ore the lime is genera generally lly prepared by the method known as dry slacking that is taking 1 the quick lime and adding only sufficient water to reduce e the lime to a fine dry powder thus prepared 7 it is easily powdered and is presented in a very efficient form the exact amount of lime necessary requires careful calculation as either an insufficient supply or an excess will give disappointing results the consumption of zinc like that of cyanide has likewise been greatly reduced within the last five years and now only from one fourth to three eighths of a pound is consumed per ton of ore treated judicious handling of the lime has an important bearing on the consumption of the zinc the surface or oxidized ores of the mercur district however present few difficulties but occasionally a pocket of ore will find its way into the tanks and therewith make its presence felt in a most objectionable way this ore contains the following minerals which affect the solution namely native sulphur the arsenic sulphides sulp hides and orpiment ferrous compounds and occasionally a certain kind of shale no chemist could suggest a more deleterious mixture for effectually checking the solution of the gold the alkaline aya nide solution acting on the sulphur and sul aphides produces a soluble alkaline sulphide in presence of which no gold can be dissolved the cause of this is easily explained gold to be dissolved by a cyanide solution requires the presence of oxygen 11 in that solution by the introduction of even a very small quantity of such a strong 11 reducing agent as an alki line sulp sulphide bide the oxygen is thereby removed and the solution of the gold rendered impossible therefore before the cyanide solution thus fouled by the presence of an alkaline sulphide can be rendered effective this sulphide must be removed either by oxidation to sulphate or precipitation as an insoluble sulphide the ferrous compounds in the base ores are also extremely injurious but act in a different way from the sulphides sulp hides namely by conversion of the cyanide into ferrous cyanide which for all practical purposes is a non solvent for 11 gold another occasional constituent the shale acts in a similar manner to the sulphide namely as s a reducing medium thereby rendering the solution ineffective fec tive this alle shale has also the property of precipitating gold gald already in solution through virtue of the carbon which it contains I 1 have taken a solution assaying 1160 per ton and after circulating it through some of this pulverized base ore for twenty six hours found it then assayed only it will thus be seen that the base ore at pf the mercur dis district is a hard combination for the cyanide process I 1 have known the entire stock of solution in several of the mills milla being run run to waste because according to the millman mill man it had become fouled by arsenic I 1 have shown by the above that this is partly an erroneous idea as the arsenic while present is not the real cause of the trouble the sulphur in combination with the arsenic the ferrous iron and the carbon in the shale are the causes I 1 have treated an ore containing over three and one half per cent of arsenic with satisfactory results but the arsenic in this case was carried in the minerals and J parities vari ties of arsenic minerals in fact arsenic is present at all times in the cyanide solution in the mercur district and is precipitated to a certain extent on the zinc with the gold i the sulphide in solution accod accounts ants for the fact that the solution after having been used on the base ore is inefficient when turned onto a thoroughly oxidized ore even although it may have had more cyanide added and the solution again brought up to the working str strength enoth 11 careful attention at the mine however can almost entirely eliminate this danger from the base when working the oxidized ores as this base ore occurs principally in bunches along the han hanging cring wall where it can be left hanging or sorted out when the workings get deeper and the base ore becomes general roasting will become absolutely necessary and this is the metallurgical lurg ical problem which will require to be decided in the near future and is being investigated vesti gated at the golden gate mill at the present time A superabundance of tale talc in the oxidized ore sometimes causes trouble in leaching but this is only a mechanical difficulty and can be obviated in most cases in the district by judicious mixing of the different characters of the ores at the mine before going to the mill to be crushed on some of the ore of the west dip of the mercur district however roasting 11 of the oxidized ore will be absolutely necessary before it can be successfully treated owing to the large percentage of talcy dalcy and clayey matter which it contains as in the case of the la cigale ore this talcy dalcy and clayey matter which is composed of hydrated silicate of magnesium hydrated silicate of aluminium etc on being roasted becomes dehydrated and in this condition leaches beautifully the objective point in treating very slimy ores ones successfully uc cess fully is to heat that ore to a sufficient temperature to expel the water of hydration combined water of the silicates and oxides when an easy leaching product will be produced the extractions obtained in the camp floyd or mercur district by the macarthur for rest cyanide process are very good considering the character and grade of ore metallurgists will agree with me when I 1 say that an extraction of 75 to 80 percent on ore and 80 to 86 per cent on oil ore is good work and that is what is being done on ore in the camp floyd district at the present time I 1 now came come to a very important point and one which will probably be of interest to all namely the cost of mining and milling by cyanide in the mercur district mining in the mercur district is being done at a cost of from to per ton and the milling from 75 cents to per ton and several of the companies in mercur are mining and milling by cyanide for less than per ton the low figure for cost has enabled some of the companies to work ore at a profit and is ample testimony to the value of the cyanide process in concluding then my remarks on the mercur district I 1 will point out the daily capacity of the cyanide mills in operation ati the present time to which I 1 will add the ca lacity of those in course of erection and which will be ready for crushing within the next two months to illustrate the great de which has taken place within the last lait five years at the beginning of 1893 the capacity of the cyanide mills in the district was fifty tons per day at the present time it is fifteen hundred tons per day but the use of cyanide has developed equally rapidly in other states besides utah in the cripple creek camp of colorado about tons per month of ore varying in character and value are successfully treated in custom cyanide mills when the process was first introduced into cripple creek fourbears four years ago r the camp wa was s in its infancy and the ore treated was almost entirely of an oxidized character which readily yielded its value to cyanide but as the camp developed the character of the ore changed becoming 11 base the values being carried in the live tellurium minerals and iron pyrites this necessitated a change in the method of treatment which was effected by first roasting theore the ore before leaching it thus overcoming the difficulty cult y and enabling 11 the process to become available for both the oxidized and base ores of the district another result of cyanide research has been to prove the thorough efficiency of the process when applied not only to ores of low grade but to gold bearing rock carrying values at four or five ounces in arizona where the cyanide process was operated in the early stages of its introduction into this country quite a number of large ores and tailing plants are being successfully operated in connection with the copper characteristics of the arizona ores oresia it was formerly generally accepted that the presence of a small quantity of copper entirely prevented treatment by cyanide but a modification modification of the process has been devised which meets this difficulty to a very large extent in one of the arizona tailing plants the cost of profitable treatment has been brought as low as 65 cents per ton on tailings which five years ago were considered untreatable untreatable considerable interest has recently been manifested by the mining operators of montana regarding the use of cyanide and at the present moment four new mills are either starting up operations or are in course of erection time will not permit me to detail the cyanide successes of california black hills idaho oregon nevada etc but the extensive use of cyanide based largely on the results of careful experiments conducted on ores from all parts ot the united states leads to the conclusion that in many cases where the first appearance of an ore does not look favorable for treatment by cyanide a judicious modification of the process under expert guidance will achieve satisfactory results one of the greatest drawbacks however in the extension of the use of cyanide is is the result which occasionally follows the starting up of cyanide operations without experienced perien ced supervision mr montgomery of colorado complained the other day and justly so of the principle prompting eastern capitalists to send out their friends who are absolutely inexperienced to take charge of mines many of these eastern representatives who might be diff diffident dent about taking charge of a mine have no hesitancy whatever in accepting 13 the responsibilities attached to the running of a mill particularly a cyanide mill as the process to the uninitiated seems to present few difficulties with the facilities which every mine owner can now have for having his ore thoroughly tested and reported upon before incurring a nickel of expense in the erection of a cyanide plant it is ig absolutely unnecessary to incur the expense of plant erection until the prospective operator knows exactly the most economical modification of the process to follow the actual extraction to be obtained and the cost per ton to be incurred in the obtaining of that extraction in other words provided the mine continues to carry the values nothing need be left to chance in the treatment of t the re ore by means of aya cyanide nide of potassium |