The classifier overflow adjusted to a pH of approximately 7.5 to 7.8 is conditioned with a stibnite activator such as copper sulfate or lead acetate and a collector such as Z-11 or a liquid type Aerofloat. Depending upon the mineralogy of the ore, other auxiliary reagents may also be required to depress sulfides which tend to float with and thus lower the grade of the stibnite concentrate. For example, bleaching powder has been used effectively for the depression of arsenopyrite and cyanide for the depression of pyrite.
The conditioner overflow passes to an 8-cell “Sub-A” Flotation Machine, arranged to provide four rougher cells, two scavenger cells and one cell for each of two stages of cleaning. The distinctive cell-to-cell design of “Sub-A” Flotation Machines permits the transfer of the various pulp streams within the flotation circuit without the use of pumps. Extremely fine talcose slimes which floated with the stibnite in the rougher cells are effectively depressed in the cleaners with the aid of a small quantity of yellow dextrine.
CONCENTRATE THICKENING AND FILTERING
The cleaned antimony concentrate is pumped to a Spiral Rake Thickener to remove excess water prior to filtering. A Adjustable Stroke Diaphragm Pump meters the thickened flotation concentrate to a Disc Filter. Where water must be reclaimed for re-use, the rougher tailings are thickened in a Spiral Rake Thickener and the plant water is reclaimed.
SAMPLING
For the efficient control of milling operations, reliable sampling is required. For this purpose Automatic Samplers are used on the heads, concentrates and tailings. A metallurgical balance is run for each shift. Sampling interval of one cut each 15 minutes has proved adequate except where quality of ore is spotty or unusual conditions are encountered.
LABORATORY TESTING
The beneficiation of stibnite ores by flotation can frequently be a difficult problem because of the complex nature of the mineral associations often encountered. It is essential, therefore, that a comprehensive laboratory test program be carried out on a representative sample of the ore before planning a milling installation.