Interface behavior of chalcopyrite during flotation from cyanide tailings

The interface characteristics of cyanide tailings are different from those of the raw ore. In this study, valuable elements could not be thoroughly recovered via the flotation of cyanide tailings from Shandong, China. The interface and floatability of these tailings were investig- ated by phase analysis and flotation tests. The chalcopyrite in the cyanide tailings was fine and had a porous surface. The floatability of 68% chalcopyrite was similar to that of galena in the presence of a collector. A layer of fine galena particles compactly wrapped the chalcopyrite. The chalcopyrite recovery sharply decreased as the nonpolar oil residue in cyanide tailings was extracted using alcohol;however, this removal had no effect on the galena. The remaining chalcopyrite in the flotation tailings was covered with an oxidation layer consisting of O, Fe, S, Pb, Cu, Zn, and Si.

Reagent elution combined with positive pressure filtration:A zero-discharge method for cyanide tailings remediation

At present, the cyanide gold extraction process is still the main technology for gold production. Generated cyanide tailings containing highly toxic substances exhibit potential environmental risks. These tailings are in urgent need of purification treatment, especially after being classified as hazardous waste. In this study, the impacts of elution methods, operating time, tailings/water ratios, reagent types on the elution rates of cyanide were investigated. Furthermore, the composite elution method developed in this research was extended for engineering. Results showed that the optimum elution conditions were determined to be: stirring elution, tailings/water ratio( M/V;1:1) and operating time(10-20 min). Besides, 4 reagents(sodium dodecyl benzene sulfonate, cyclodextrin, sodium silicate and calcium hydroxide) were selected from four categories of 21 reagents for further composite elution. The cyanide elution rate was the highest(90.7% ±0.1%) while the molar ratio of these 4 reagents was 5:2:2:1. Moreover, the combination of reagent elution and positive pressure filtration improved the elution efficiency of cyanide(92.6% ±0.8%). And the cyanide content in the toxic leaching solution was lower than the standard value(5.0 mg/L). Furthermore, the composite elution method developed in this study was also extended for engineering. The concentration of cyanide in the leachate was < 5.0 mg/L, and was stable during 189 days of detection. Notably, the effluent can be reused directly, or reused after further treatment. The zero discharge of effluents and solid wastes was realized in the processes. The above results provided supports for the engineering treatment of cyanide tailings.

Pretreatment of cyanided tailings by catalytic ozonation with Mn^(2+)/O^3

The increasing amount of cyanided tailings produced as a by-product has gained significant attention in recent years because of the rapid development of the gold industry and extensive exploitation of gold mineral resources. The effective use of these secondary resources is becoming an important and urgent problem for all environmental protection staff. Manganese-catalyzed ozonation for the pre-oxidation of cyanided tailings was studied and the effects of Mn2＋dosage, initial sulfuric acid concentration, ozone volume flow, temperature and agitation speed on pretreatment were examined. The optimum reaction conditions were observed to be： ore pulp density 2.5%, agitation speed 700 r/min,temperature 60°C, Mn2＋dosage 40 g/L, ozone volume flow 80 L/hr, initial sulfuric acid concentration 1 mol/L, and reaction time 6 hr. Under these conditions, the leaching rate of Fe and weight loss could reach 94.85% and 48.89% respectively. The leaching process of cyanided tailings by Mn2＋/O3 was analyzed, and it was found that the leaching of pyrite depends on synergetic oxidation by high-valent manganese and O3, in which the former played an important part.

High-temperature chlorination of gold with transformation of iron phase

Gold in cyanide tailings from Shandong Province is mainly encapsulated by hematite and magnetite at distribution rates of 76.49 % and 10.88 %, respectively.Chlorination-reduction one-step roasting of cyanide tailings was conducted under the following conditions： calcium chloride dosage of 6 %, bituminous coal dosage of 30 %, calcium oxide dosage of 10 %（all dosages are vs.the mass of cyanide tailings） at 1000 ℃ of roasting temperature. X-ray diffraction（XRD）, scanning electron microscopy（SEM）, and chemical-phase analysis were performed to investigate the effects of iron phase transformation on the high-temperature chlorination of gold.Results indicate that the lattice structure of hematite undergoes expansion, pulverization, and reorganization when hematite is reduced to magnetite, which leads to42.03 % gold exposure, and the high-temperature chlorination rate of gold is 41.17 % at the same time. The structure of wustite formed by the reduction in magnetite is porous and loose, and thus 44.02 % of gold is exposed. The high-temperature chlorination rate of gold is increased by41.98 percentage points. When wustite is reduced to metallic iron, 4.42 % of gold is exposed, and the hightemperature chlorination rate of gold is increased by3.38 percentage points. Accordingly, the high-temperature chlorination of gold mainly occurs in two stages, in which Fe_2O_3 is reduced to Fe_3O_4, and Fe_3O_4 is reduced to Fe_xO finally.