Study On Arsenic Removal From Arsenic-Contained Copper Ores By Combined Selective Flotation And Hydro-Leaching

Arsenic-bearing minerals are prevalent in copper deposits,which mostly exists in the form of tennantite and enargite.In 15%of the world’s copper resources,the ratio of arsenic to copper is as high as 20%.Arsenic-contained copper minerals will access the copper concentrate through conventional flotation process due to its highly similar floatability with associated arsenic-free copper minerals,which causes a great negative impact on under-stream smelting.Thus,arsenic removal from copper ores is a challenge for many companies and researchers.It is of great significance to improve and clean copper smelting production if arsenic can be removed from arsenic-bearing copper concentrate before entering the smelting system by efficient technology.In this paper,Zijinshan copper ore,a typical arsenic-bearing copper ore enriched with enargite,digenite and covellite were studied.The difference in flotation behavior between enargite,digenite and covellite was studied and the floatability of several minerals after selective oxidation was confirmed,which provided a theoretical basis for selective oxidation and flotation separation of copper and arsenic.Based on the previous study,a proposed process including flotation separation of high-arsenic copper concentrate after selective oxidation followed by selective leaching was comprehensively studied with Zijinshan copper concentrate.Consequently,a technical route about arsenic removal from arsenic-contained copper ores through “selective oxidization in flotation separation-selective leaching of high-arsenic copper concentrate-arsenic solidification from leachate” was developed,which provides an efficient way to treat high-arsenic copper concentrate in a green and clean manner.Some important observations from the conducted research work were described as follows:（1）The flotation behaviors of digenite,covellite and enargite were studied in the absence and presence of various additives.Effects of oxidants including Ca（Cl O）₂ and KMnO₄,and organic depressants like sodium humic acid and lignin on the flotation behavior were investigated under different pH values.The results indicated that strong oxidants could effectively inhibit digenite and covellite from flotation,meanwhile enargite could still keep a decent floatability.Contact angles were tested and revealed that the contact angles of digenite reduced from 90°to 15°～23°after oxidized by Ca（Cl O）₂,while the contact angle of enargite was still more than 86°,which enlarged the difference in floatability significantly between digenite and enargite.XPS results indicated that sulfur on the surface of digenite was oxidized to SO₄^2-,and copper on the surface was oxidized to Cu（Ⅱ）ion that covered the mineral particles as hydrophilic Cu（Ⅱ）O/OH.Enargite existed stably and kept the surface hydrophobic in the presence of Ca（Cl O）₂.TOF-SIMS analysis showed digenite surface was oxidized more easily than enargite,which caused the decrease in intensity of ADD on digenite was greater than that on enargite.The thermodynamic results showed that when the pH value was10～12,digenite and covellite were oxidized to Cu₂O at low solution E_hwhile enargite existed stably.Tafel curve studies demonstrated that the E_corr（V）values of covellite,digenite,and enargite were-0.40V、-0.38V and 0.20V respectively.The antioxidation capacity of enargite was stronger than those of covellite and digenite,and surface oxidization occurred on digenite and covellite were prior to that of enargite under lower solution E_h.Under lower solution Eh,covellite and digenite were more easily oxidized to be hydrophilic while enargite was quite resistant to oxidation with the hydrophobicity well maintained on the surface.（2）The effects of selective oxidization by calcium hypochlorite on the following flotation separation of copper and arsenic were tested with Zijinshan arsenic-bearing copper concentrate.High-arsenic and low-arsenic copper concentrates were obtained through a series of operations including flotation agents removal by activated carbon,selective oxidation and flotation separation with the addition of 600g/t calcium hypochlorite and 100g/t humic acid sodium.Low-arsenic copper concentrates consisted of 0.40%Asand 18.20%Cu,and the recoveries of arsenic and copper were 29.3%and 78.33%respectively.High-arsenic copper with a arsenic concentration ratio of 6:1contained 7.47%Asand 38.48%Cu and the recoveries of arsenic and copper were 21.67%and 70.7%respectively.（3）Researches on selective leaching to remove arsenic were carried out with high-arsenic copper concentrate arsenic leaching efficiency was over 99%under the optimized conditions of 200g/L of Na OH,190℃,180min,and a liguid/solid ratio of 5m L/g,while copper was almost undissolved.XRD analysis showed that enargite transformed into some new copper sulfide minerals,including Cu₇S₄,Cu₈S₅and Cu₃₁S₁₆,which realized the selective removal of arsenic from high-arsenic copper concentrate.（4）Arsenic solidification from leachate was studied.Firstly,AsS₄^3-was oxidized to AsO₄^3-by adding oxidant H₂O₂,then selected precipitants MgCl₂ and NH₄Cl were added to precipitate AsO₄^3-.It was found that 99.97%of arsenic ions precipitated when the dosage of oxidant H₂O₂ was 3 times equivalent to the stoichiometric amount and the molar ratios of Mg/Asand NH₄/Aswere 1.6/1 and 8/1 respectively at the solution pH values of 9.5,and the residual arsenic in leaching solution decreased to 1.8mg/L.