Especiação de cianeto para redução do consumo no circuito de lixiviação de calcinado da usina do Queiróz

• Ano de defesa: 2005
• Autor(a) principal: Walter de Moura
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais; UFMG
• Palavras-chave em Português: Especiação; pré-lime; cianetação; Engenharia metalúrgica; Hidrometalurgia; Lixiviação
• Link de acesso: http://hdl.handle.net/1843/BUOS-8DJHXK

Queiróz Plant, located in Nova Lima City, Minas Gerais State, Brazil, treats a semi refractory gold ore of approximately 7 g/t of gold from the Cuiabá Mine. The ore is milled, 30% of the gold is recovered by gravity concentration, and floated to produce a pyrite flotation concentrate with a gold grade around 30 g/t. The final tonnage of concentrate depends on the sulfur grade, which varies from 3 to 9% in the ore. The concentrate is roasted to liberate the gold locked in pyrite. When the amount of concentrate produced is higher than the roaster capacity it is sent to cycloning. The underflow goes directly to roasting and the overflow, which contains pyrite and some pyrrhotite, goes directly to the leaching circuit. The gold of these fines are recovered by cyanidation in a blending with the calcine produced in the roaster. The cyanide consumption is high, approx. 2.5kg/t of calcine, costing about US$ 300.000/year. Aninvestigation was carried out to reduce cyanide consumption in this circuit. The results showed that cyanide is consumed metal cyanocomplexes (50% of the cyanide consumed), mainly zinc and copper, and thiocyanide formation (31%). As demonstrated in laboratory, the presence of the zinc cyanocomplex is not deleterious to cyanidation, since the complex is an effective leaching reagent for gold. The irreversible loss of cyanide as thiocyanide is associated to the by-pass of the sulfide fines directly to the leaching circuits. Addition of lead nitrate did not reduce either the thiocyanide formation neither the cyanide consumption. The results also showed that increasing the pre-lime time to the range of 10 to 16 hours and increasing the lime addition in the pré-lime to the range of 10 to 13 kg/t of calcine, it is possible to reducethe cyanide consumption between 22 to 45%. This result was correlated to the reduction of cyanocomplexes formation and implied in operational savings between US$ 15,000 to US$ 63,000/year (5 - 20% of the total costs with cyanide). Further savings would require the elimination of both situations: fresh sulfides by-pass the roaster and copper sulfate addition in the flotation circuit.