TREATING AURIFEROUS ORES.

Inangahua Times, Volume X, Issue 1631, 25 November 1885, Page 2

TREATING AURIFEROUS ORES.

IMPORTANT DISCOVERY.

Tlifc British mining papers contain long accounts of what is designated the, Cassel Gold Extraction process, which, if successful, mnst exercise an important influence on the gold mining industry throughout the world. One of these papers, Iron, prefaces it 3 report as follows : — " One of the uiosf; serious drawbacks to successful gold mining is th« difficulty of treating ores when associated with pyrites, arsenic, antimony, and oilier ietYaet<.ry substances. In the upper strata the gold is usually found in a free condition, aad is easily obtained after reduction either by washing or l>y amalgamation with mercury. In the deeper workings however, the gold U generally met with in a refractory condition, and is a source of trouble and absolute loss. In some cases each I grain of gold is enveloped in a skin of

sulphur or of iron oxide, which ' effectually protects it from the action j of the mercury, over which it quietly glides away out with the tailings. In ' other cases the association of thegoll '; with other metals, as already indicated, | is the great bane. Tims it comes to ; pass that many a good yielding gold mine has come to grief simply becanse I there were no means of wresting the ' gold from its unworthy and l»y fur too intimate associates. Chemistry ha", however, done something to remedy i this condition of things, and the Plattner clilorinisution process affords one means of weaning the precious metal from if 3 evil ways. In thi3 process thp ores are roasted to drive off the snlphnr, and are then steeped fur a considerable tune in a vat into which chlorine gas is continually fed. The gas rises through the wet moss, attacking the gold, and converting it into the chloride, which is very sohiMe. Wh*n this action is complete the mass of ground ore is waslied witli hot water , to ivroovfr tho sotab'to ehlorMp, which is nf^erwai'ds precipitated in the form of black mud, and melted inucrnciMe. Tin's process is carried out when the circumstances are favourable, and to bo favoraWo it is said that there mu^t be several mines in immediate proximity to one another, as it is out of the question to . carry the ore far, and the tailings must be rich, as the chlorine, even when ample time i 3 allowed, \ fails to penetrate the ore so completely ( as to reduce the whole of the gold. ' The cost of freight for the chemicals has also to be considered in wild countries and out-of the<way districts." For these reasons the process has only a very limited application, and the great bulk of the refractory ores are thrown away, Indeed, a competent authority has said thai in the various

gold producing districts there are. millions of tons of refractory ores awaiting the discovery of a cheap, simple and effectual mode cf treatment. This may seem an exaggeration ; but in Australia we have an abundance of auriferous ground neglected simply because the ores are too refractory to pay the cost of treatment.

But if the Casscl process is really what it is described as being, these now valm-li'ss properties will become fairly and even hLhly remunerative. According to Iron, the process is the invention of Mr Henry R Cassel, and is being practically worked by the Cassel Gold Extracting C >mpany, of Glasgow. It is also a chloiinisation process, but the evolution of the chlorine and the precipitation of the gold are effected by the agency of electricity, nnd as this can be generated by mechanical means, it follows that an immense stride has been made in the way of simplification. Farther the chlorine is produced in immediate contact with thp ground ore, and nnfse f s upon it while in the nascent condition, when its affinities are in a condition of maximum activity. At the same! time, nascent oxygen is also generated, winch, oxidising the sulphides, arsenirUs, &c, liberates the gold, the nascent chlorine at once converting it into a tei chloride.. A secondary reaction here takes plnce, and hypochlorous acid is formed, which oxydises the pyrites. Hydrochloric acid is also formed, which" attacks any iron present, nnd forming a protosalt of that metal, this soluble iron compound precipitates the gold as fast as the chlorine brings it into solution, and thus prevents its extraction. " This," (says Iron) " was the difficulty which btffled previous investiga^rs in this direction, but which has been ingeniously and succesfully overcome by Mr Cassel. Others may have succeeded in dissolving all the gold from the ores, and yet were always unable to find any in eolation.

Mr Cassel recognising, after many experiments, the complicated nature of the reaction which so puzzled his predecessors, and being the first to point it out, hbs at length devised means whereby the iron compounds which are invariably present in refrao- | tory ores are retained in their insoluble

form while under treatment, and thus are prevented from exercising any inflaence npon the solution of gold.

This he accomplishes by the addition of canstic lime to the mixture of crushed ore and salt, which earth, by reason of its alkaline properties, at once combines with any free hydrochloric aoid as fast as the latter is formed, and completely neutralises it, so that no iron can l>e taken up. At the same time a hypochlorite of lime is formed, which, again being decomposed hy the action of the water present, affords additional nascent chlorine f«r the gold ; the ultimate products of the reaction l»eing — chloride of sodinm in excess, chlorid of calcium, tri chloride of gold and andecompO3ed gangue at the anode, and chloride, of sodium and sodium hydrate at the cathode." The news of tb*» process awakened considerable interest in British mining circles, and recently th«* apparatus hy which it is carried into effect was inspected by a number of practical metallurgists and other gentlemen interested in gold mining. Among those present were Sir Hussey Vivian, Sir Charles Tennant, Sir Hugh Low, Professor Chandler Roberts, Professor J. Forbes, Dr Hugo Miller, Mr J. Arthur Phillips, Mr. Warren de la Rue, Mr. Mathey, Mr. M'lll wraith (brother of the ex-Premier of Queensj land), and othets. The demonstration j was conducted by Mr. Cassels, assisted :by Dr Henry Liepmann and Dr. Rowland J. Atcherley, who have aidtnl , Mr. Cassel in the experimental ad\ , practical development of the process i In pi-rti.tii c. the concentrated ore is t placed in a revolving drum capable of containing a charge of 2£ tons. T.> | the ore is added a quantity of silt { water. Inside the drum are a series j of carbon electrodes through which a j current is passed from an ordinary ; dynamo machine. Soon after tie ! drum is started the lime is mld»d. By

the electrolytical action Hip sulr is ; decomposed, and the nascent chloride (as well as the oxygen) is given off at ' tlie carbon anodes. The chlorine combines with the gold, thus forming a solution of chloride of gold. From! that solution the electrolytical action ; carries it into a perforated central tube, w!ii..'i forms the axis of the di-nni and wlji=:!i is covered with asbestos \ cloth. The gold is deposited in a finely divided metallic stat<? on the ; interior of the tube which forms the cathode. T!jc fiuiction of the lime is to neutralise the acifles which wonid i be formed !>?-« 4^-y-uHry action, and '■. which would aitfflfe the iron, aisonio, , or other metals - which might be. present in the ore, forming salt 3of I those metals, which would precipitaro the gold wi*ro tlieir fiM'nid.ioi] not pr«- ; vented, thus undoi'ig all th.- previous work. liisifletheperfotatedcontrat tube iff an Hrchiinedean screw, which k««ps the waterutidothercotiti>n(snf the drum iii circulation, carrying l\r:? %oh\ r\\minto a rfiifiwer, where it is deposit^H by gravitiition. This slime is drawn olFat intervals, dried, aivl the g--»hl recovered by smelting in the. usnal way. •' Such," says Iron, •' is Mr. Cassel's interesting process, and such the means by which it is carried out. The result so far is ; unquestionable success, and we fail to | discover any reason why it should not i sneceed am perfectly on a practical and t commercial scale. According to most j recent theories, it is held that gold and others metals have been deposited in the fissures of the earth's crust from their solutions by electrochemical action. It is known that all sea water contains an appreciable amonut of gold in solution (about one grain to the ton of water), and also probably that thi3 lms been originally dissolved by the chlorine of the sea

water from the rocks of the earth t>y a similar action. Hence it is only reasonable to assume that a process brin^ing nature's own great factors into operation would be the mrans of redissnlviu.iT that siiWstance which it pieviously had deposited and dissolved under the same conditions. We can ; i»ut wish the Cassd process that snecess

it merits, and which, wh think, it

is destined to achieve. It is based on

souii'l scientific an-1 p: 1

■a-^tical principle?,

and is readily adapted to the. reqnire-

tncnts of the gold mining industry."