|
TREATMENT OF SULPHURET ORES AT CHARACTERISTIC MIXES. 137
gamation. These plates are interchangeable; whenever the upper plate becomes hard and unfit for amalgamation, it is interchanged with one of the lower plates, thus giving in rotation to each plate a position at the head of the table. The outside amalgamation-surface of each battery is further increased by 12 additional square feet, arranged by a drop system of three plates, the pulp discharging from one to the other before it enters the main launder. Each battery is provided at the screen-discharge with an impact-plate, not only for amalgamation, but to retard the velocity of the pulp. They are cleaned from verdigris with a weak solution of cyanide, and a little potash is sometimes fed into the battery. Phosphate of sodium is used in the mill to keep the quicksilver bright and lively. It has been found expedient to remove the inside plates every 24 hours; as duplicate plates are kept on hand, no delay occurs while they are being cleaned. The amalgam from these, which is collected and weighed daily, forms an excellent indication of the value of the ore milled. The amalgam is removed from the outside plates whenever it is necessary. A regular clean-up is made only once a month. About one-third of the gold is saved on the inside plates. The fineness of the mill gold is 880. The average amount of water used per stamp is 3-J gallons a minute; and the average consumption of quicksilver is 0.35 ounce per ton of ore. The wear of shoes and dies is 1.3 pounds per ton of ore stamped. As a lubricant for the cams, molasses thickened with flour is used and gives excellent results.
The pulp is carried to the concentrators in launders lined with riffles for a distance of eighty feet. No attempt at sizing the pulp is made, but the ores from the Beguelin and Cross mines, owing to the difference in contents of sulphurets, are concentrated separately. The Cross ore averages about 2 per cent., the Beguelin running from about 7 to 25 per cent, sulphurets. They are milled separately in the proportion of XV Beguelin and xw Cross, so as to obtain an average of 7 to 8 per cent, sulphurets from the total ore milled. The concentration is done on 20 Embrey tables (4 by 12 feet), with smooth rubber belts which are set at an inclination of 2f inches and travel 5 feet per minute, receiving at the same time 192 percussions. The concentrates contain 90 per cent, pyrite, which is pure sulphide of iron with occasional small traces of arsenic. The loss in concentration is 15 to 20 per cent. The average value of these concentrates is $25 to $35 per ton.
Chlorination. The concentrates are hauled on the mine-railway to the chlorination plant. They are roasted in two double-hearth reverberatory (see fig. 27) and one revolving pan-furnace, the sulphur being reduced from about 43 to as low as \ per cent., and the value of the material being increased by Tj. Each double-hearth furnace is worked by two men to a shift of 12 hours, the output being 2 tons of roasted
|
||
|
|
||