Research on the speed of metalic release and arsenic behavior
in water at the tailing dump
Lê Thu Thủy, Trần Hồng Côn,
Nguyễn Thị Cẩm Hà, Nguyễn Thị Thục Anh
Arsenopyrite is a very common mineral that is associated with metallic minerals, hydothermal genesis, often associated with other sulfuric minerals. In tailling waste dump, arsenopyrite is affected by weathering and releases arsenic (As) element into the environment. In the areas where Cu, Pb, Zn mineral... are exploited, the problem of pollution to the environment is a big concern, which should be treated thoroughly. This reaseach shows the ability to release arsenic and heavy metals during weathering from arsenopyrit ores tailing dump but it is caried out in laboratory scale model, in drench and submerged conditions, similar to those on the ground, ore content in the sample was 5%, duration of experiment was 60 days, thereby identifying the presence of As in the different chemistries. The results show that under water infiltration conditions, the pH value decreases during the experiment and the oxidation depletion potential ranges from 5 to 50 mV, metals and arsenic are released into the environment, depence on increasing over time with the pH decreases. When the pH is reduced to meet with the pH value of the acid discharge (pH = 2-4.5), the rate of weathering is noticeably faster. Under submerged conditions, when dissolved oxygen is high, metals are freed faster; but then decreases, in this condition pH is in ranges of 5.5 to 6.0, so when the ore is oxidized, iron exist in the form of Fe (II) and then slowly oxidizes to be Fe ( III). At the same pH as above, Fe (III) hydrolyses in the iron (III) hydroxide column and arsenic released are adsorbed on Fe (III) and at the same time, the amount of Fe (OH)3 formed will cover ore particles, made reducing the contact between the waste ore and the water environment, the arsenic concentration continues to decrease. The results of this study also show that in both cases of drench and submerged, As (III) is more dominant than the As (V) in the effluent from the ore column. As (III) bring a potential to be highly toxic in the environment, so attention should be paid to change to As (V).
Keywords: Arsenopyrit, water, infiltration, submerge, As(III), As(V).