Leaching of Trace Amounts of Metals from Flotation Tailings in Cupric Chloride Solutions

With decreasing ore grades, the tailings of mining operations are becoming of increasing interest as metal-containing secondary
raw materials. The objective of the current work was to investigate chloride leaching of gold, copper, cobalt, nickel, and zinc
present in the flotation tailings. In the current study, the effect of cupric ion as an oxidant (0–50 g/L) and NaCl (150–250 g/L) on
metals extraction was investigated. The other parameters, such as pH (1.8), temperature (95 °C), solid/liquid ratio (25%), oxygen
feed rate (1200 mL/min), leaching time (24 h), and stirring rate (950 rpm), were kept constant. Gold dissolution rate was shown to
increase with increase in cupric ion concentrations up to 50 g/L. Also, increase in NaCl concentration up to 250 g/L increased
gold extraction. Majority of the copper present in the flotation tailings could be dissolved with all the all solutions investigated.
The other base metals, cobalt, nickel, and zinc extractions were also shown to increase with increase in the cupric ion and sodium
chloride concentration. However, even in the absence of cupric ion addition (t = 72 h, 250 g/L NaCl), the final extraction of Cu,
Ni, Zn, Co, and Fe increased up to 98, 93, 83, 76, and 80%, respectively. This shows the power of inherently originating oxidants
present in the tailings. Furthermore, the solid analysis of the leach residue indicated that leaching the flotation tailings in pure
NaCl may result in partial gold dissolution. The results demonstrate that significant amount of metals present in the tailings could
be extracted even with only NaCl as added chemical in the presence of oxygen feed, oxidizing agents originating directly from
the raw material. This can provide an advantageous cyanide-free method for extraction of metals from very low-grade tailings
with low chemical consumption.