Show flotation concentration in 1916 BY A B PARSONS continued increase in the general widespread application of the process a steady but not phenomenal refinement in the technique of operation and some approach toward a scientific treatment of various problems relating to the art this briefly is the progress of flotation concentration during the year 1916 the scientific entine investigators are no nearer a generally accepted theoretical solution of the question why or what is flotation than they were a year ago much has been written in an effort to prove by a course of reasoning that this theory or that application is tenable to the exclusion of others but the fact remains that no one has yet actually proven that his theory is entirely sound possibly this is due to the fact that actual experimental research has been substituted too generally by purely mental speculation based on doubtful hypotheses phenomenon of surface tension certain physical phenomena are of necessity involved in any explanation of the process we would not have froth flotation as we comprehend it today without the froth or in other words the bubbles bubbles are accounted for primarily by what we call surface tension so that one factor in flotation is the physical phenomenon of surface tension adhesion is another factor which cannot be left out of consideration for there manifestly must be adhesion between the metallic surfaces the surface of the air bubble and that of the contaminant supposedly oil of the water further this adhesion must operate selectively in favor of the surfaces as opposed to the surfaces of gangue materials gravity of course plays its very essential part as it does in everything else but outside of these three physical principles surface tension adhesion and gravity we are indulging to a greater or less degree in metallurgist salt lake city utah theoretical speculation in an effort to entirely account for flotation phenomena number of variable factors it is safe to say that we do not know what flotation really is or just how the various elements of the process are ae dependent pendent upon any set of conditions it follows that in considering the method of applying the process to a given ore it is still necessary to make extensive empirical tests to determine the most suitable and economical conditions for operation the comparatively large number of variable factors will include the following method of fineness of grinding dilution of pulp the degree of acidity or alkalinity the kind of oil or ores the amount of oil or oils temperature conditions and the air pressure to be maintained in a pneumatic 11 cell or the impeller speed of a mechanical machine since there appears to be a decided absence of any general rules that can be laid down each individual ore is a distinct problem in itself which should be worked out by an expert an unusually large number of experimental tests improvement over other systems the cautious investigator in stating any conclusion which we may have reached in variably qualifies fles his statements with some such clause as with this particular ore or under the conditions at this plant at the same time it is a fact that there are practically no instances in which flotation properly employed will not make a material improvement over any system of straight gravity concentration on copper lead or zinc ores and it likewise has been applied successfully in the treatment of gold silver mercury and molybdenum this is one of the outstanding features of the process that while almost every concentrating ore is amenable to flotation a different combination of important details is required for nearly every ore and methods which give maximum results on one will result in utter failure when applied to another ore of seemingly similar character this is more or less to be expected of course in view of the admitted scientific mystery which surrounds the entire subject what Is flotation slime has no terrors As stated the process has been found applicable to practically any ordinary concentrating cent rating ore the one great point wherein it surpasses the old gravity operation is in the treatment of the slimed portion of the crushed ore the metallurgist has always recognized the fact that his losses were largely in the slime tailings that is until he began to float now his slime has no terrors instead of spending effort and money in crushing with a minimum of sliming he devotes himself to getting the crushing done efficiently and cheaply quite regardless of what proportion of his feed is slimed he can recover as much as ever on his jigs and his sand tables and the remedy for the tine fine product is flotation to date this is perhaps the most import aint application of the process the replacement of the inefficient slime concentrating devices in mills where the flow sheets formerly included banners and various vario us so called sl imers combinations of flotation units the possible combinations of flotation units are almost unlimited and dozens of ingenious and effective flow sheets are in operation the fact must not be lost sight of that flotation is really an admirably simple efficient means of obtaining similar but generally better results than can ibe be accomplished on gravity concentrators and can be installed to perform any appropriate step in a scheme of concentration tabling of flotation tailings A step farther is the adoption of a straight flotation treatment or one where flotation is followed by tabling of flotation tailings As a general proposition the advantages of such a system are several construction costs are small for given capacity recovery is highly satisfactory water consumption is minimized operation cost for both power and labor is low and simplicity throughout the plant is obtained this holds good in practically all departments the crushing is simplified classification fi and watering de are to a large extent eliminated and the number of operations erat ions is reduced to a minimum quite frequently flotation tailings especially ally from pneumatic cells are tabled to recover coarse concentrates which the froth may have dropped there are of course some considerations which make a combination of gravity and flotation methods more satisfactory and like any other metallurgical problem the solution is simply the plan that will produce the maximum excess of production over cost flotation of oxidized ores an interesting development but one that has only recently been practically applied is the flotation of carbonate and oxidized ores this can ibe be done toy by a preliminary treatment to film the ore particles with a sulphide coating when properly coated the carbonates of lead and copper have been quite successfully floated although efforts to handle zinc carbonates have not met with much success as yet schemes for forming the sulphide film include the use among other things of hydrogen sulphide gas solutions of calcium and sodium compounds of sulphur and ted oils the latter method with crude petroleum and sulphur treated on the ground in specialty specially designed apparatus has been used to film copper carbonate ores at an extremely moderate cost and subsequent flotation operations have given highly satisfactory results on a large scale it is of interest to note that some attempts to small portions of oxidized copper minerals in a sulphide feed by the addition of sodium sulphide resulted in failure of the entire flotation the operators are at a loss to explain the reason the fact that there are vast quantities of low grade carbonate ores on which the old gravity methods of concentration have been employed with indifferent success makes the field a particularly alluring one and further progress in this direction may be anticipated in the near future differential flotation differential flotation involves the regulation of conditions so as to float one of two valuable minerals present in an ore to the exclusion of the other a subsequent operation being employed to recover the second mineral constituent an example which illustrates the general principles involved is given in one of the lAine minerals rals separations patents an ore contains along with the gangue galena and frothing with the proper amount of acid will remove most of the copper and very little of the lead and zinc A second operation with the addition of sulphuric acid and increased oil separates the galena and from the tailings of this treatment can be floated the by the addition of olele acid this is of course an ideal case and the lines of sepa artion are not clear cut so that the various products require further treatment or treatment re to produce concentrates of marketable grade in australia lyster has patented a process wherein varying proportions of certain sulphates chlorides nitrates and other salts added to the pulp so modify conditions as to make possible the flotation of galena from an alkaline solution with only a very small percentage of the contained the latter is floated later with the introduction of additional oil in this country a combination of flo tation units and gravity concentrators is commonly employed to accomplish a separation of the and galena in numerous zinc lead concentrators develops develop ment of simpler methods for effecting similar results may be expected flotation and the flotation of precious metals is confined largely to ores wherein the gold and silver are associated with sulphide minerals but there already is keen competition with in treating this class of ores it can obviously be applied either in conjunction with amalgamation and gravity concentration or where fine grinding is essential to liberate the sulphides sulp hides a straight flotation concentration followed by or smelting smelling sm elting of concentrates concen rates is quite possible some complications are at once manifest in the cyaniding cyan iding of flotation concentrates arising from the presence of even small quantities of oil but a practical solution of the difficulty will doubtless be developed gold telluride ores in colorado have been very successfully floated and numerous old tailing dumps are being worked reworked re at the present time apparatus for frothing apparatus for the actual frothing naturally divides itself into two classes depending on the two methods of getting finely subdivided air into the pulp viz by violent mechanical agitation as exemplified by the mineral separation standard machine and by introduction of the air under low pressure through a porous medium following the plan first devised by callow dozens of machines and cells as the pneumatic type is styled have been developed ve loped but with little essentially new while it is unwise to attempt generalizations in connection with the process there are certain characteristic features of the mechanical and pneumatic methods which recent practice has made clear permanency of froth generally speaking the froth formed in the pneumatic tid cell is less permanent and stable than the mechanically made froth this is an advantage in that there is less difficulty in subsequently killing the froth for handling the concentrates but there is also a disadvantage in that the recovery of the coarser particles of mili mineral eral is not so complete this however is not particularly serious as the coarse concentrates are readily recovered by subsequent tabling with gravity concentrators on the other hand when operating at full rated capacity the purely mechanical machines in some instances at least fail to effe effect C t as complete a recovery of the very fine material as do the pneumatic cells this fact has its results in the hibbard type M aa S machine and the janney machine where the pneumatic feature has been combined with mechanical agitation the pneumatic type the pneumatic type appears to have an unquestioned questioned LIn advantage both as regards cost of installation and power consumption for a given capacity this advantage is accentuated where the introduction of oil and other agents can be effected ahead of the machines a chines this is not always possible so that additional equipment is sometimes required for intimately nixing mixing the oil and pulp the callow machine while many modifications of the original callow pneumatic cells have been made with probably some advantages in manipulation nothing has been found to supplant callows original plan of several layers of loosely sewed canvas twill as a porous medium the inspiration cell consists essentially of an enlarged gently sloping launder divided by baffles extending to within a few inches of the bottom into sixteen compartments approximately three by four feet A pulp overflow in the middle has the practical effect of forming two cells in series the entire box is made of steel and the bottom boi lom for introducing the air is a separate unit and can be simply lowered into place oace from above this bottom consists of an air t ht cast iron fron shell the tor of which a grating which supports the canvas A conforming steel spider is is bolted on top of the canvas and holds it in place A centrally located perpendicular air pipe extends up through the bo body d y of each compartment the purpose of t the h e baffles is to prevent accumulations of sa sand n d in the bottom of the cell by constricting the area of flow at intervals the upward passage of the tailings is assured toy by the introduction of an air jet at the end of the last compartment and the regulation of pulp level is automatic suitable launders catch the froth overflow on each side of the cell the machine is self contained is certainly simple and gives results which are said to equal if not surpass the callow cell on some ores the crerar machine another machine which appears to have some merit was designed by george crerar it consists of a set of six narrow cells six feet long set side by side with parallel troth froth launders between betwee ll each pair short pipes near the bottom connect alternate ends of each cell with the adjoining cell so that the flow of pulp passes the length of all of the cells the successive cells are each three inches deeper the re autant hydraulic head causing the flow through the machine each cell is fourteen inches wide and the canvas used as the porous medium is simply tacked unstitched to the under side of the cell walls with halt half round steel pan bottoms bolted against them no reinforcement is required for the canvas low pressure air being supplied as in the callow machine substitute for float valve an unique substitute for a float valve to regulate the pulp level consists of a gate valve and a stand pipe whose height can ibe be altered by the turning of a tee at the bottom of the last cell the gate valve is opened slightly to allow the passage of heavy sand which might otherwise cause clogging and the regulation is effected by means of the stand pipe which carries the bulk of the pulp this device has one apparent advantage the maximum flow ol of froth is only seven inches one half the width of the cell which would seem to make possible a less stable and consequently more easily handled froth it would seem to he be extremely simple in construction and operation disposal of concentrates the question of disposal of concentrates has been given considerable attention it is s necessary to make a product as low as practicable in moisture and a de watering plant is a necessary adjunct to a flotation installation not invariably the case a filter is generally required because the fineness of the material increases its tendency to hold moisture A dorr thickener and a filter of the oliver type make the most usual combination the kelly pressure filter is used with good results in a number of plants the thickeners are best fitted with a high annular baffle extending it a short distance beneath the surface of the water to hold the froth and prevent contamination of the overflow it recently has been found |