Sulfuric acid slag, also known as pyrite cinder, is a solid waste generated during the production of sulfuric acid by pyrite roasting. The gold minerals in such slag are usually fine-grained and highly encapsulated, leading to low gold recovery rate in traditional grinding processes, along with high energy consumption, high cost and serious resource waste.
The combined process of ultrafine grinding by vertical stirred ball mill and flotation-cyanidation can break through the technical problem of fine-grained gold dissociation, achieving a gold recovery rate of more than 90% and a 30% increase in comprehensive benefits.
The specific process is as follows:
1.Crushing & Pretreatment (Raw Ore Preparation)
Gold-bearing sulfuric acid roasting slag is crushed and screened to about 10 mm, then transported to the silo by belt conveyor. If the slag has high sulfur and iron content, oxidative roasting or acid leaching desulfurization shall be carried out first to improve the dissociation degree of gold minerals.
2.Primary Grinding & Classification
The raw material is fed into the ball mill for rough grinding, forming a closed circuit with the spiral classifier, and the pulp with 55% of -200 mesh is produced. The sand returned by the classifier is sent back to the ball mill for regrinding, the overflow product is pumped into the high-efficiency thickener for dehydration, and the underflow is adjusted to a concentration of 35% for standby.
3.Ultrafine Grinding by Vertical Stirred Ball Mill
Grinding fineness is the key factor affecting gold leaching rate of sulfuric acid slag. Gold in sulfuric acid slag is micron-sized and encapsulated in pyrite, hematite and other minerals, which needs to be fully exposed by ultrafine grinding. The thickener underflow enters the vertical stirred ball mill with 0.5% sodium hexametaphosphate, and is ground to 90% passing -400 mesh. Tests show that this fineness can increase gold leaching rate from 72% to 93%. The vertical stirred ball mill and hydrocyclone form a closed circuit, with overflow entering flotation and underflow returning for regrinding.
4.Gold Flotation Concentration
Butyl xanthate and pine oil are added to the roughing pulp, the pH of the pulp is adjusted to 8.5 with lime for flotation, and the gold-bearing sulfide rough concentrate is obtained. The rough concentrate is subjected to two stages of cleaning (the tailings are returned to the roughing process), and finally the flotation concentrate with a gold grade of 45g/t is obtained.
5.Cyanidation Leaching & Gold Recovery
The flotation concentrate is fed into the agitation leaching tank, 0.1% sodium cyanide solution is added, the pH of the pulp is adjusted to 10.5, and aeration leaching is carried out for 24 hours with a gold leaching rate of more than 92%. The pregnant solution is replaced with zinc powder to obtain gold mud, and the tailings enter the tailings re-selection process after preliminary washing.
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