MERCURY EXTRACTION

Evening Post, Volume CI, Issue 128, 31 May 1921, Page 2

MERCURY EXTRACTION

NKW ZEALAND EXPERIMENTS.

Mercury is chiefly, obtained from the ore. known, as .cinnabar, or mercurons sulphide. It is found in various places in New Zealand/ among others, Pnhi' puhi. Cinnabar is a red material, which, in a pure form, is the wellknown pigment vaf mil lion. The* usual method of treatment is to roast the ore in a furnace, when the mercury is vapourised and can be more or less com-< pletejy condensed from the flue-gases. At a meeting of the Wellington' Chemical Society, Mr. W. Donovan read a paper on an interesting process of cinnabiti %'eatme.nt recently developed to work the Puhi-piihi cinnabar. This ore is not very rich, and it also breaks up to such an extent as" to clog the furnaces. It has ben found within the past few years, Mr. Donovan explained, that cinnabnr can be dissolved in what is^ called "Thornhill's solution," made by dissolving 4 per cent, of sodium sulphide and 1 per cent, of caustic soda in water. Variation in the proportions of the chemical'used'altered the extent to which the cinnabar was soluble. Mr. Donovan pointed-.out that to use such a solution to ' treat the mass of ore and gangue would be very costly; either a great deal of the solution would be lost, or there would be.gieat expense in lecoveiing-. it. An attempt was therefore made to concentrate the cinnabar, and it was found that (being very brittle) it became so finely divided, that the ordinary washing processes used in ore concentration resulted in much of the mercurjf ore being floated away. Experiment/* were then made with the oil-flotation, process. This consists in shaking uji the ore with Water and oil to form a' froth ;. and the. result is that though the ore is heavier than the stone, the latter sinks in the water, and the cinnabar floats in the froth.' Development of the process showed that if certain chemicals were added, the amount of oil (eucalyptus) required is very, small. Puhi-puhi cinnabar thus treated gave a concentrate of one twentyfifth of the original bulk, containing 88 pay oeill. of the cinnabar. . This rich concentrate could be economically treated witih Thornhill's solution. The recovery of the mercury from the solution was an American practice done by tho use of aluminium scraps, which were oxidised and lost. As aluminium1 was too costly in New Zealand for the purpose, electrolytic separation was tried, with a carbon anode and a mercury cathode. This was successful, but the separation could not be hurried, aa both; voltage and <:urrent density mwr.t be Very low. i

Mr. Donovan said there was still work to he done in bringing these processes to the best practical shape for tho local conditions, but it had been suspended till it had been ascertained whether the Puhi-puhi deposits contained enough1 cinnnabar to justify the laying down of a large plant. The. lecture was illustrated by several experiments illustrating the oil-fldtation/ process.