Show review 0 ew of chani Cyan cyaniding iding di ng in 1 n 19 1916 16 BY P al mchugh there has been but little advancement made in during the past year most of the plants built have been along standard practice one or two plants have however increased their efficiency by changing to the all slime treatment and several new continuous countercurrent counter current decantation plants have been erected A year ago many operators believed that flotation would take the place of but this has only proved the case on certain characters of ore it is really difficult even at this date to determine just what influence flotation will have on the cyanide industry although it would seem as if plants treating ores carrying a high percentage of sulphides sulp hides or ores of character may be greatly benefited by the use of flotation this is evidenced by the results obtained by the argo reduction ore purchasing company as well as others which have changed from to flotation with most gratifying results these conditions however were just reversed at a well known plant in the cripple creek district where a large flotation plant was plaD planned ned it was found in treatment that the ore was to a great extent oxidized and could not be handled successfully by flotation the result being that they are now erecting a 1000 ton plant to treat the ore by the first experiments that were apparently successful were conducted on sulphide ores but when flotation was attempted on ores containing both oxides and sulphides sulp hides it was demonstrated that conditions favorable to the flotation of the sulphides sulp hides would not give satisfactory results on the oxide portion and vice versa the goldfield consolidated installed a ton flotation flo unit but at the present writing it is not known whether the process has proved successful except in the treating of the sulphide ores in districts such as cobalt where flotation would be used instead of the problem of refining the recovered concentrate cen has proved serious concentrates from this district generally contain antimony arsenic and nickel thus making the refining cost high the matter of flotation testing is a very important feature as it is not always possible to show results in practice corresponding to the flotation test work there have been several marked examples of this difficulty fi but with further development of flotation it may be possible to show what causes this divergence from cyanide tests it is possible to tell quite closely the re suits that may be obtained in mill practice denver colorado general manager of the e dorr company many problems presented there are many problems to be considered in the installation of the f flotation lo tation process on gold and silver ores such as plants which are located at some distance from the railroad thereby making it necessary to ship their concentrate in the case of cyanide plants this problem is simplified in that they can ship the bullion direct it is unlikely that flotation will replace on gold and silver ores where there is not sufficient base metal to produce an increased revenue from the concentrate except where the ore may be of a refractory nature and not amenable to cyanide treatment the cost of bullion recovered by flotation is often greater than the cost of bullion recovered by the cyanide process and at one plant it was estimated that an additional extraction of 5 per cent was required on the ores when flotation was used to break even with the cost of eya many of the methods of handling pulp in the flotation process have been adopted from cyanide practice such as crushing in closed circuit with classifiers thickening the pulp before flotation and thickening flotation concentrate by means of dorr thickeners on the other hand some of the cyanide plants installed during the past year have been adopting ball mill crushing which is used largely in flotation mills in place of stamps and other grinding mediums development during the coming year will doubtless demonstrate more clearly just how far it is possible for flotation to replace eya the cost of supplies during the past year the cost of supplies has had a serious effect on the cost of operation of cyanide plants and at the present time there is a great scarcity of cyanide and the ready supply available is selling at an excessive figure which will require the closer attention of the operator to mechanical ch losses of cyanide in the process careful attention to these losses will mean a greater recovery in the dissolved value losses also the development of the dorr tray thickener which will greatly cut down the size of thickeners required in cyanide plants will prove a valuable adjunct in the initial cost of cyanide plants in the future such plants as the hollinger consolidated gold mines company which in the near future will be treating in the neighborhood of tons of ore per day have greatly reduced the cost of their plant by means of the tray thickeners the tray thickener A A brief description of this machine will undoubtedly undoubted lybe ibe of interest consider the dorr thickener installed in a tank in the usual manner and midway between the top and bottom of the tank an additional spider with arms attached is keyed to the central shaft A sheet steel bottom sloped to conform to the slope of the arms is suspended from the periphery of the tank ank an opening of about a two foot circle at the center of the tray allows free passage of the pulp between the compartments different types of these trays are used for different conditions and character of ores but the most widely used type is called the connected type in which the thickened discharge is taken from the center of both the tray and the bottom of the tank mhd overflow from the tray is taken off by the regular peripheral overflow launder and the overflow from the lower compartment is at the periphery of the tank just below the tray bottom at one point the tray bottom at the periphery acts as an inverted overflow launder owing to its slope the feed to both compartments enters at the center of the tank in the usual feed or loading well the detailed study of slime settlement and the control of slime by E G free 0 C ralston G H clevenger H S coe paul W avery and A AV allen alien has been of wonderful assistance to all operators in wet metallurgy this theoretical study has great practical value and there has been more development along this line than in the ten years previous A change of solution A development which has been going on during the past two years has shown the advisability on a great many ores of making a change or solution during agitation and the extraction has been materially benefited at such mills as the rochester gold II mining ining company of rochester nevada and the pittsburg dolores mill at yerington nevada A direct comparison could be made at these mills owing to the fact that the operation was started without a change of solution and later the flow sheet was changed so that this could be accomplished there has been a number of other plants where this has also proved successful and in the writers opinion the extraction on any gold or silver ores will be bettered by making this change of solution it is very difficult however in testing work to show just what can be accomplished first because it is difficult to maintain enough old solution to keep using the same solution over and over again and second because in handling the small quantity of solutions which are used in testing work the absorption of oxygen by these solutions is much more rapid than in mill practice and tends to give the same result as a change in solution A brief description of some of the cyanide plants which started operation or were continued on page 49 REVIEW OF CYANIDING continued from page 46 under construction during the past year may be of interest united eastern mill oatman arizona this is a ton all slime plant after coarse crushing by means of a gyratory crusher the crushed material is delivered to ball mills which discharge to callow screens the oversize is returned to the ball mill for further grinding the undersize passes to three additional ball mills using small balls these mills are arranged in closed circuit with dorr classifiers A separation not exceeding 10 per cent plus mesh is desired the overflow from the classifiers passes to the continuous current decantation system in which a change of solution is made during agitation this is accomplished by interposing a dorr thickener between the third and fourth dorr agitators merrill zinc dust precipitation is used the plant is designed so that the capacity can be doubled at comparatively small expense hollinger consolidated gold mines company timmins ontario the enlargement of the hollinger mill to tons per day gives canada the largest continuous countercurrent counter current decantation plant in the world after initial crushing by stamps the product is delivered to tube mills arranged in closed circuit with dorr classifiers the overflow from passes to a series of 40 foot tray thickeners each of which handles the product from two tube mills the overflow from each tray thickener is delivered to two 30 1 0 foot dorr agitators after agitation the entire pulp passes over single deck delator deister concentrating tables the tailings from which pass to continuous countercurrent counter current decantation decant atlon each unit of which contains four 40 foot tray thickeners the concentrates from the delster deister tables are elevated to tube mill for re grinding thence to dorr agitators from the agitators the reground concentrate concen rate joins the pulp going to continuous countercurrent decantation merrill zinc dust precipitation I 1 is used the barnes king development company marysville marksville Marys ville montana this mill has been increased to tons per day and changed from partial leaching to all sliming it is of interest in that they allow two changes of solution during treatment lane mills are used for the coarse grinding the product from which is elevated to classifiers the discharge passes to two sets of wilfley tables the tailings from which pass to two foot tube mills arranged in closed circuit with dorr classifiers the overflow from the classifiers passes to the continuous countercurrent counter current decantation system consisting of both standard and tray thickeners the first change of solution occurs between the fourth and fifth agitators the second change of solution takes place between the fifth and sixth agitators the discharge from the fourth or last thickener goes to the portland filters zinc shavings are used for precipitation the bannack gold mining company bannack montana this plant has just been completed and is expected to start operation in the spring the ore after passing the farrel crusher is elevated to the crushed ore bin from which part of the feed is delivered to ten stamps and part to one foot ball mill the product from both stani stamps s and ball mill passes to two foot tube mills arranged in closed circuit with dorr classifiers the product from the classifiers passes to continuous countercurrent counter current decin decantation tation one change of solution takes place between the first and second agitators from the second agitator the pulp is delivered to a series of four 28 foot dorr thickeners and finally to waste zinc shavings are used for precipitation the plant is carefully designed and the capacity can be readily increased |