Beneficiation of Auriferous Pyrite from Wynaad, Nilgiris

Abstract

Beneficiation of three samples of auriferous pyrite from the abandoned mines of Alpha and Harewood situated in the Wynaad area of Nilgiris, Madras has been studied, primarily with a view to utilizing these as sources of sulphur. Samples A and B from Alpha mine were found to contain 1.7 and 1.46 percent sulphur and 0.06 dwt./ton and traces of gold respectively. As the principal gangue minerals in these samples are of low specific and gravity, tabling has given concentrates of low grade 37.8 to 39.3 percent sulphur , recoveries being 62.1 and 72.7 percent. Optimum conditions for the flotation of pyrite have also been worked out. Recoveries of sulphur are over 90 percent by flotation and the concentrates grades vary from 39.8 to 47.1 percent sulphur. The sample from Harewood mine was highly weathered and complex from the point of view mineral dressing. It was found to contain 2.4 percent sulphur and 3.7 dwt. of gold per ton. Sulphur is present in the form of pyrite, pyrrhotite, mercasite and sulphates. Flotation recovers 50 to 64 percent sulphur. It is evident that the low sulphur, the contents of the samples make them uneconomical as sources of sulphur. The possibility of recovering gold and some of the sulphur as a by-product from the ore from Harewood mine was also studied, a detailed study of the various factors which affect the dissolution of gold in cyanide solutions being made. Optimum particles size for cyanidation has been found to be 65 mesh. Use of lead acetate accelerates the dissolution of gold. Direct cyanidation of the ore after removal of magnetic minerals at -35 mesh result in lower consumption of cyanide. Flotation of pyrite and gold, followed by roasting of the floatation concentrate at 750°C and cyanidation of the calcine recovers 92.0 percent of the total gold, with a cyanide consumption of 0.21 1b./ton of ore . There is thus some possibility of economic utilization of the Harewood deposits.