Show the simpler methods of concentration concen tra ti BY LEROY A PALMER E M it is not an uncommon occurrence to read in a newspaper especially in the west that some old mine long ago abandoned as worked out is to be reopened on a larger scale than ever or that some mining property which for years had been a graveyard of fortunes is now returning comfortable dividends to its shareholders this great progress in the mining industry is due not only to the improvements in mining methods but even more to the great strides made in the sister science metallurgy one of the chief branches of which is concentration this is a preliminary process by which ores too low in grade for treatment at the smelters shelters sm elters are prepared to be smelted smelter at a profit ind and which forms the chief of the various milling processes it is as the name implies the concentration of the valuable portions of the ore into smaller bulk by the elimination of the waste material th the e object is twofold two fold first the reduction in in bulk to save the cost of transporting and smelting smelling sm elting the larger quantity of ore second and more important por tant the charges for smelting smelling sm elting an ore are based on the proportion of metallic contents to waste so by reducing the quantity of the latter the smelting smelling sm elting charge per ton is materially cut down in some cases to the point where the smelters shelters sm elters actually pay for the privilege of treating certain ores the process is so simple that the mill men of today look back in wonder at the century of development that was necessary to bring it to its present state of perfection the treatment is entirely by mechanical means and is based on the principle that a particle of mineral being largely metallic and therefore of greater weight will offer more resistance to a current of water than a particle of waste of the same size which is lighter being composed of some form of rock commonly quartz technically called silica it is thus seen that the successful treatment of an ore requires that all of the particles treated on the same machine must be of approximately the same size and to accomplish this 4 A I 1 Q the ordinary type of jig tain crushing and sizing apparatus is necessary I 1 the ore as broken down in the mine varies in size from pieces weighing a hundred pounds or more to a powder this is all conveyed to the concentrating mill and dumped into bins containing grizzlies grizzlier grizz lies slanting parallel bars of railroad iron which allow the iane fine ore to pass th through rought the coarse sliding down the bars to a gate in the front of the bin to be fed into the crusher this consists of two heavy corrugated steel plates of rectangular shape one stationary and the other swinging the ore is fed between these plates or jaws and crushed to pieces about the size of ones ones fist by the impact of the swinging jaw the crushed product usually discharging into the bin beneath the grizzly the crushed ore is fed from the bin for further crushing in rolls two heavy rolls with chilled steel shells between which the ore passes the object of this crushing is to break the ore sufficiently fine to disengage the mineral from the waste with which it is associated if the ore is very hard or the metallic portion is in fine particles further crushing in rolls is usually necessary before the ore is sized for the concentration proper the sizing is done in or revolving cylindrical screens each of which has a different mesh the ore as it comes from the rolls enters the upper end of the first where it is mixed with water to aid in carrying it through here it separates into undersize which passes through the meshes and oversize which passes through the and out of the lower end the being slightly slight lk inclined from the horizontal the undersize passes to the next of the series which has a finer mesh and the process is repeated the oversize of each is therefore between the mesh of its screen and the one preceding so in this way the ore is very closely assorted as to size the oversize from each goes to a jig of w which the hartz is the most typical form the body of the jig is of V cross section and about nine feet long four feet wide and four feet deep it is divided h laterally into three compartments each compartment being divided lengthwise by a partition extending about half way to the bottom on one side of this partition is a screen of a mesh which will just allow the particular size of ore that jig is to treat to pass through on the other side of the partition is a plunger which receives a vertical reciprocating motion from an eccentric water rater being led into the jig the plunger forces it up and down through the screen over which the ore passes the stroke and speed of the plunger is varied to suit the size of the ore the coarsest jigs making about one hundred and twenty one and one half inch strokes per minutia minute and the finest jigs as high as four hundred and eighty the stroke being so short as to just impart a quiver to the water the ore is fed to the jig at one end and immediately meets the pulsating current of 0 water the mineral particles being heavier settle to the bottom faster than the waste and pass through the screen thence through a discharge orifice out of the jig as concentrates in order to prevent their settling too fast and dragging waste with them the screen is covered with coarse Ini mineral through which they must pass before reaching the screen As there is not time for all of the mineral to settle out in the first compartment this process is repeated on the second and again on the third hut but here the product is somewhat different the upper layer of ore which by this time should consist almost entirely of waste passes over the lower end of the jig ji and is discharged to the dump as tailings but as it is impossible to effect an absolutely clean separation the operator allows part of the waste to pass through the third screen so as to reduce the loss of mineral in the tailings to the lowest possible point this mixed product is called and as it often contains ore in which the mineral has not been entirely broken away from the waste in the previous grinding special re grinding processes are frequently necessary A typical re grinding machine is the chilian mill in which the ore is ia fed in at the top and ground by large steel shod rollers running in a circle and discharged when of sufficient fineness to pass through the screens in the side of the mill the product of the chilian mills and the undersize from the last are now run to hydraulic classifiers for sizing before being treated on the tables the classifiers are boxes into one end of which the fine ore flows in the water with which it is mixed in the bottom of the box is the discharge pipe in which is a T a stream of water flows into the T part of it passing into the classifier and setting up an upward current against which the ore must settle to pass through the discharge 4 f AMP na table wilfley pattern pipe that which cannot settle passes on to the next classifier where the U upward p ward current is not so strong and so on until all but the extremely fine ore is assorted each classifier discharging its sized product to a table the wilfley table consists of a linoleum covered deck fifteen feet long six feet wide at the head or feed end and five feet wide at the tall tail or discharge end and sloping 1119 gently from back to front this deck is covered with riffles fiffles rif fles narrow strips of wood spaced one and one half inches apart varying in length from four feet at the upper head corner to the full length of the table at the lower edge the ends of the riffles fiffles making a diagonal line across the table the table has a longitudinal shaking motion of about two hundred strokes per minute and is kept bovere covered d by a thin sheet of water flowing across it from the back the ore is fed on the corner where the riffles fiffles are shortest to the ends of which the heavy metallic particles cling while the lighter waste washes onto them the shaking motion aids in the separation and works the ore down to the tall tail of the table the mineral discharging over the end as concentrates and the waste over the side as tailings As in the jigs it is imps i ri chilian mill sible to effect a perfect separation so a portion of of the ore areis is discharged as mid clings into a third receptacle and retreated on the same table being raised by wheel elevators passing the tables we reach the great problem that confronts the millman in crushing the ore it is inevitable that some of it breaks break svery very fine in some cases to pieces so fine that over forty thousand are of which has a bottom shaped like an inverted cone in which the slimes settle and thicken before being drawn off for treatment on the banners van ners the vanner consists of an endless rubber belt six feet wide passing over two rollers twelve feet apart thus presenting a working surface six by twelve feet the belt travels up an incline and at the same time receives a side shaking motion of about two hundred strokes per minute the slimes are fed on near the upper end in thin streams from a box extending the width of the belt and just ahead of which is a similar box discharging in wash water which covers the belt in a thin sheet as on the tables the metallic pa particles tend to cling to the rubber surface against the action of the water while the waste is washed to the lower end to be discharged into the tailrace tail race As the belt uns runs r over the roller at the higher end a spray of water washes the concentrates into a box placed to receive them and the scheme of concentration has been carried as far as is customary in ordinary practice there are a great many machines for handling the ore in the various stages of concentration but each of those just described is typical of its class there also are many other machines common in all mills conveyor belts and elevators for transporting the ore pumps for handling the water and such others as specific conditions malce make necessary and which do not come strictly under the head of concentrating machinery it would be impossible to estimate the ra IL Y ariy riy wilfley slimer required to cover a square inch As the mineral portion of the ore is the more brittle these fines or slimes as they are called are usually quite rich frequently assaying higher than the ore as it comes from the mine but the individual particles are so light that they either float out of the last classifier or go to the tables in huspen suspension sion offering no resistance to the wash water they are carried across the head end to a receptacle provided for them they arl are ml all colle collected ebed in round tanks each value of the process of concentration to the mining industry the millions that have been rescued from old dumps and low grade mines to be returned to the stockholder the machinery man and the laborer and the end is not yet for at almost every mill one finds that the tailings dump is being carefully preserved awaiting the day when genius or some lucky luchy accident will find a way to save the insignia insignificant cant values which at the present time it is impossible to keep from froin going to waste |