Extraction of Gold from Pyrites.

Cromwell Argus, Volume III, Issue 131, 14 May 1872, Page 7

Extraction of Gold from Pyrites.

On this subject, Mr E. A. Kayser, writing to the Ballarat Miner, says :—" Mr Harry Koch, of Bendigo, has erected a machine fur j extracting gold from pyrites, and he has been | rewarded for his enterprise. I know for a j fact that he got out of five tons of blanket j tailings from Menzies' New Chum, as much j as 18 ozs. 6 dwts. of gold, and the quartz was not nearly so much stained with mundic and pyrites, as it is on this field below the waterlevel. His process is the following :—The pyrites having been separated from the sand, is taken to a heap, and thence put into a sort of hopper, whence it falls upon the floor of the furnace for burning. This furnace is in the shape of a half pyramid, built of the best fire-bricks. It rises one foot in height. At the lower part is situated the fire-place, two logs being sufficient to keep it going after the furnace is thoroughly heated. The fire runs through the structure to the top, and, being arched close, the flame as it passes up is thrown upon the pyrites, which is spread upon the narrow space, and kept continually turned by men with long-handled rakes through small loop-holes in the sides, thus presenting it to the action of the flames in such a manner thut it is thoroughly roasted, and the arsenic, sul j phur, &c, driven oil'. The moving also! causes the pyrites to fall down the incline, j and it gradually moves on until it drops through a small aperture near the fire into a space, whence, thoroughly burned, it is taken away to undergo the third and most important process. "Having been burned, the pyrites, which before that process was of a blue colour, but is now rusty red, is taken to the house containing the grinding pans (Wheeler's) and there put into the pans. These are more difficult to describe. Around the pan are fixed between the outer edge and the standard plates, knifes, or whatever one may call them, which are curved and converged into the centre, where two faces meet when the standard is turned round, and between these two iron faces the pyrites passes and is ground, going down underneath, and then by the action rising up through an aperture round the outer edge, and being brought down to the iron faces again by the action of the pyrites, for the plates do not move, but guide the pyrites into the centre where the grinding machinery is at work, so that they may be said to run in a circle. After the pyrites is ground for some time, and is supposed to be ready, a certain amount of quicksilver is mixed with it, and the grinding process is repeated until the quicksilver is thoroughly mixed with the pyrites. The pyrites and the quicksilver now pass, when they are supposed to be ready, into an amalgamating pan filled with water, which is continually stirred. The quicksilver containing the gold sinks to the bottom, while the water carries off the dross into a small huddle, designed exactly like the one described. The floor of this huddle is covered with copper, and this catches the smallest particle of silver which may have escaped, allowing the other matter to flow away. "It may be as well to mention a few important particulars concerning the furnace. In burning pyrites the great objection is the effect of the arsenical fumes in poisoning the air. Mr Koch's mode to prevent this is as follows. The flame, after passing up the passage referred to, on the floor of which is placed the pyrites, has to go back underneath this floor in another flue, and heats the floor on which the pyrites is spread. It then goes up another passage underneath this again, having thus 102 feet of a passage in the furnace before passing out of it. From the furn; ce the flame passes to a square chamber close to the chimney-stack of the crushing machine. Upon the flame when it enters this chamber a multitude of small jets of water are poured, causing the condensation of all the poisonous matter, and their precipitation to the chamber in the form of white powder, while the vapor, cleared of all obnoxious particles, passes off up the chimney with the other smoke."