Show theory PUR and practice ablat of ore C concentration by flotation 11 discussion of 40 vital IRIA features of jo this all important subject by A W M fahrenwald ore dressing ic aua engineer jagaut the discovery of JO the d property i of jo the ore dio minerals when V agitated 0 with water jda containing a small ab nb quantity of 10 uc an oily substance to ol zUlu attach Ll themselves with varying 0 degrees of JO tenacity to 01 the otil nu air bubbles formed by the dili elbe agitation boll and to 04 selectively concentrate au in U a froth on the surface of jo the D ore dlo water jalm pulp proved to 01 be the birth of lo a process that IMP sull has completely revolutionized methods of JO ore dressing it II si is about twelve years ago since bouls the daj isau first mill ul in this country was designed bisp 0 adul and built for boj concentrating ore by this now mon there iu diu are D probably alq ou no less than tons sul of 10 ore treated by the process IM yearly X the all property A of 10 the various common minerals to 01 show different capacities to 01 absorb or ao 10 collect 10 oily X substances ud on their surfaces so and show a selective tendency to attach themselves to 01 PUL and be lifted by bubbles proved to be a difficult one duo to 01 control when applied lit in practice it 11 was sum difficult for the operator and for the experienced su as well to 04 understand why two apparently wis similar ores when subjected to 01 apparently ebud parallel conditions with regard to 01 kind pul and quantity of jo reagents used and 2 agitation 1 etc gave dae quite different results v although now mou we DA dau are able to oi control loii the dai delicate but inq 1 positive factors SI involved to 01 a degree dds sufficient to ol make the process applicable PUL and available for the dili ii treatment of the aali sio ores qi the D mystery of jo the physical or io possibly chem lz tut cal mechanism involved adal si is not IOU entirely 4 absent and the dill metallurgist who loav having aj tried PDT to 01 p develop dola the dill theory of jo the DOid process ss and then alq having zul stood pools by waiting for the dili j 0 ja 0 q trained 14 physical chemist to 01 show him the dill W only to ol be disappointed SIDDI feels OU no embarrassment over ls amo past and id present ludsy inability to oi un understand the theory of JO old flotation d carding laa the theory of jo flotation space will not IOU permit v that 1 41 bears the meres pretense of 10 covering the oal q e used ui in the practical present day subs lon as scheme DIU a of jo two general selo classes SS 1 organic put and da pine oils duld nine lul tars s aull hardwood P creosote P al I 1 tar distillates substances adz etc PUI and 2 ioui inorganic class of jo ass 1 are frequently among those tens sl as aou on polar substances inq but they lower the surface sorna 1 water and dau are therefore presumably os soluble to 04 effect eluam ent for only soluble or ao partially soluble substances ahe a al surface tension of JO water they are aiu therefore polar Is s ial that it jhc thc molecules have soluble portions or radi lp oils sl of jo water very 0 lower dal e surface tension A oil tion ly A le the SHO oils derived ij from LUO the destructive jo 0 im coal lower D it J to 01 a less marked degree pul and DIL are there 9 fl tl stivis of JO differential flotation goodau 18 JO IS ina aai in ot jo i 1 ja t mi W ne serial no 2700 dept o of 0 commerce fore ID presumably alq less soluble ut in water adlum than the pine or hardwood oils table I 1 1 oils therefore djojo since 0 change eq dau ui in ins surface tension sa s1 is EMP always ax accompanied by adsorption adsorb cl on the OT bubble water s surfaces n and idd permit allu the dili building up of jo a ii froth 1110 this then si is one duo useful function of jo oil 10 ua in the notation zoid process table I 1 N minimum surface tension of jo mixtures of lo some common j flotation oils and water lu at 26 C dynes per centimeter A water u 4 ad I 1 steam distilled pine oil 10 j hardwood creosote eucalyptus s oil 10 camphor po oil coal juo tar creosote DIOSO oleic acid it 11 should however not IOU be understood that lulli the ins surface i aou tension of jo the surface of jo a freshly boj formed patu bubble in u a ij flotation pulp st is of jo the dili same magnitude su as the surface tension of JO the free surface daijo of the pulp or io su as the ins surface tension bols of JO the dill JI froth alio llio formed on top dol of jo the pulp the ins surface tension of jo a fresh or io newly formed surface such su as a C skimmed surface or io that of jo a u rapidly traveling bubble ST is lit 41 DI less than eill that I of jo the pure dind water A small piece of jo a sulphide mineral placed at the bottom of jo a breaker containing a solution or io mixture of jo a small amount of jo a flotation oil 10 ui in water may autu be picked paled up by a freshly formed bubble formed ju at the dill pua end of jo a capillary tube the same piece dowd of jo mineral I shows less friendliness to ol a bubble buba of jo greater age 01 1 low 0 at bubble ns surface 1 duj tension ua seems then to ol be not IOU desirable for boj best flotation too ool much oil 10 in u flotation flou or 10 I 1 over oiling gives mol low bubble surface tension and poor flotation results because it 1 destroys the selectivity AllS XI of JO bubbles s for aal mineral particles surface reactions ut in q flotation experiments seem to 01 ell have DA shown that minerals C adsorb gosp cl collect on their surfaces oil io molecules or io possibly small or jo adsorbed or io alloo collected pajo at the and the alli amount to oil 1 cloap droplets SIDI the mineral m water ins surface uj appears dmd to 01 be dependent upon chemical composition and crystal structure of jo dili the mineral the difference dud ut in the edep capacity apo of jo the dill various common definitely to 01 q bear iud u relation minerals to 61 collect loz loDi oil lio appears the pulp which bubbles introduced into with to ol the dill ease to 01 j the surface of jo the particles mineral pick up and carry bauz X pu dand minerals quartz for example and UI n the qa co case Ds of jo gangue to ol for example the property the aal sulphide minerals galena L I 1 A J k 11 IV ft vol ii ni aweau 1111 ul in JI flotation Flotat iop 1924 collect or adsorb oil and attach to air bubbles is of such wide difference as to permit a selective flotation of the sulphide minerals from the gangue minerals however in the case of the sulphide minerals themselves the difference in in this property while reasonably marked is not ordinarily sufficient to permit the sharp separation by flotation required in practice it is therefore to ca cause use a more marked difference in oil collection and bubble attachment capacity between such minerals that the substances of class II 11 always strongly pol polar ar substances are used in flotation it has been shown by experiments that oil molecules capable of lowering the surface tension of water are composed of portions or atomic groups of unequal solubility this unequal solubility of the various atomic groups composing the molecule results in a definite orientation of the molecule on the waters surface the soluble end or portion of the molecule is drawn into the water while the insoluble portion is rejected and exposed to the surface this reasoning points to an orientated orienta ted arrangement of oil molecules adsorbed at a bubble water interface fig 1 is intended to indicate graphically the arrangement of ad 7 Z 7 Z Z 71 7 Z 1 I A A 6 Z 7 AE fig 1 left showing arrangement of adsorbed oil molecules at a water bubble surface fig 2 right showing a probable arrangement of adsorbed oil molecules at a mineral water surface sobbed oil molecules at the water air bubble interface for example the molecule may be one of the formic acid series in which case the soluble hydroxyl oh groups are drawn into the body of the water while the insoluble methyl CH groups point outward and are at the surface there is no definite experimental evidence as to the nature of the adsorption of oil at solid water interfaces but in view of the orientated orienta ted arrangement of molecules known to exist at water air interfaces and at liquid liquid interfaces it is reasonable to assume that the arrangement of oil molecules adsorbed at the mineral water interface also is ori enta ted if the adsorption on the mineral surface is of such a nature that the water in soluble insoluble portion of the oil molecule sticks to the water while the water soluble portion attaches itself to the mineral surface as shown in fig 2 the explanation of the attachment of the mineral particle to the bubble would not be difficult the particle simply would be engulfed by the bubble see fig 3 similar to the floating of a piece of paraffin on a water air surface the magnitude of the tendency of the air to displace water at the oiled mineral surface or in other words the force of the air water interfacial tension would readily take hold of the particle if the oil molecules are attached atta phed to the mineral surface in the reverse order fig 4 the attachment ment if there would be any of the mineral particle to the air bubble is not so easily explained perhaps the degree of orientation of the adsorbed oil molecules on the mineral water surfaces is different for the various miner minerals ils and perhaps the value of substances of class TI II in differential flotation is due to the effect that these ionized st substances betances bs have upon the orientation of the oil m molecules adsorbed on the mineral surfaces experiments show definitely that adsorption and orientation of oil molecules at a water air surface is materially affected by the pr presence of various ions in the water also while experimentally there is not the vol volume u m e of reliable evidence the adsorptive capacity of various solid substances for oil is altered by the presence in solution of various varius iora ions A definite theory as to how flotation works is needed to say that the value of the addition of a certain chemical to fro a notation flotation pulp is caused by a chemical reaction results resulting 1 in a selective coating of the mineral surfaces due to the i formation of a new chemical compound is insufficient lt if may be and no doubt is true that selective mineral surface coating is brought about by the use of certain chemicals and that the normal order of of the respective 1 minerals has been changed but we still have to account for the new relative for the same reason we have been striving to account for the natural relative of quartz and galena or any other minerals success depends on certain conditions from the writers study and observations of ore flota tion he believes that the following conditions exist and ire are required for successful flotation 1 A low surface tension of the liquid film forming the network net work of bubbles in the froth 2 A high bubble pulp surface tension i e C when the bubble is in the body of the pulp its surface tension 1 should be high nearly the same as pure water 3 A aj large contact angle between water water of the ore pulp and the solid to be floated and a low contact angle between water and the solid desired not to float substances of class I 1 discussed above ful fulfill fill requirement no 1 andia not used in too large amounts do not interfere with requirement no 2 they act selectively to promote requirement no 3 substances of class II 11 do not in interfere with requirements nos 1 and 2 but they do promote requirement no 3 just how they do this remains to be fully explained the rapid development of the art of flotation is due to the persistent and untiring efforts of many individuals schools government bureaus and particularly to the companies who have been confronted with the necessity of turn in binl for their source of ore supply to the large deposits deposit 01 complex sulphide ores that have for years resisted thear the ordinary methods of ore dressing experience soon taught that for best metallurgical 1 re suits it was necessary to control carefully such factors 11 3 fl 1 the fineness of the grinding fa 2 the pulp density 4 the afi the quantity of oils and reagents added t to 0 the pulp W 5 j time of conditioning the pulp with the reagents and y the nature of the agitation and aeration of the conditioned condition j pulp pull W LC za d olle oile fig fie 3 left showing nature of attachment of an particle to a bubble x of nf addor adsorb fig 4 right showing improbable arrangement 01 molecules at a mineral water surface t it can be said that one of the reasons for the f of e and ard much of the earlier practice to give the recoveries grin ff of products desired was definitely due to insufficient minera i Is ing to unlock the gangue minerals from the ore nt f one and the ore minerals in case two or more were pres pt lants I 1 from another in many of the differential flotation flot atio gracent cent P of operating today the ore is ground so that eighty pe p gr it will pass a mesh screen the improvement in grinding is larg largely bely due duea to IMF riding in ment in classification the necessity for finer gri 6 beroll peris called for classifiers having larger settling setting ar area settle ca to and to of sufficient time for the smaller particles to seu cope with the tremendously large Z capacities now handled in many of the mills the dorr bowl classifier met with success the new requirement it must however be pointed out that continued grinding of the ore particles after liberation of the respective minerals has been effected is not only not necessary but expensive practice excessive grinding beyond what we may term the economic points results in 1 low grinding mill capacity 2 high grinding cost per unit of ore 3 low notation flotation machine capacity and 4 hib high h reagent consumption and poor grade products this then places a burden on the classifier operated in closed circuit with the grinding mill it should return to the ball mill the least possible amount of undersize and at the same time not permit oversize to pass with the overflow to the flotation system further requirements imposed on the classifier are 1 it should give a pulp overflow not too dilute for direct flotation which means that very little water may be used and 2 it must return a thick 80 to 90 per cent solids sand product to the grinding mill even under these restrictions better classification will eventually come noteworthy developments in flotation practice two of the most noteworthy developments in flotation practice in recent years are 1 the sheridan griswold Griz wold galena differential flotation process calling t for the use of sodium or potassium cyanide in an alkaline circuit and 2 the use of sodium and potassium xantha tes the use of a suitable flotation oil and insignificantly small amounts of sodium or potassium cyanide and a few pounds of sodium carbonate per ton of ore treated permits the flotation of 9 galena alena to proceed while the content of the ore almost completely remains in the pulp and is floated in a subsequent flotation treatment by the addition of copper sulphate Xantha tes both sodium and potassium are powerful flotation promoting agents A fraction of a pound per ton greatly helps the flotation of the sulphide minerals xan chates like the cyanides cranides cy anides in the sheridan griswold d process are used in conjunction with oils with every advance of the flotation process gravity concentration has suffered coarse jigs have been almost completely routed and in many instances table concentration has given way to all flotation methods some of the advantages of an all flotation plant are 1 simplicity of construction and operation 2 low first cost per ton of ore to be treated 3 large tonnage can be handled on a small floor space 4 complex ores require a very fine initial crushing and if part of the mineral must be |