铜冶炼污泥形成机理及其特性

Formation mechanism and characteristics of sludge in copper metallurgy plant

运用XRD、ICP-AES、AFS、TG-DSC与毒性浸出试验研究了铜火法冶炼中石灰-铁盐法处理酸性废水(污酸)过程中含重金属及砷的污泥(中和渣)形成机理和特性。结果表明:电石渣乳中主要成分Ca(OH)2与污酸中硫酸反应生成CaSO4.xH2O并成为污泥的主要成分;重金属离子主要通过水解反应被沉淀下来,而砷以砷酸盐及亚砷酸盐沉淀而去除,在pH=12.4时电石渣乳与污酸一次中和反应之后,主要有害元素从103～102mg/L降低至1 mg/L左右,经过絮凝剂添加、浓缩固-液分离与多次空气氧化步骤后使得主要重金属含量达到10 2mg/L数量级,实现净化后水质达到GB 4913—85污水排放标准;污泥随着温度的升高而逐渐失重,室温至160℃时污泥中自由水与CaSO4.xH2O结晶水依次脱除,温度至400℃左右污泥中砷氧化物升华,至600～800℃范围内少量碳酸钙发生分解,至1050℃以上CaSO4在开始分解为氧化钙并造成明显失重;毒性浸出实验中污泥浸出液中As与Se的浓度明显高于GB 5085.3—2007所允许范围,属于危险废弃物。

The formation mechanism and characteristics of sludge（neutralizing slag） containing heavy metals and arsenic from acidic wastewater（waste acid） in copper metallurgy plant were studied by using XRD,ICP-AES,AFS,TG-DSC and toxic leaching tests.The results showed that the main sludge component,CaSO4.xH2O,was formed in the neutralizing reaction between the main carbide slag emulsion component,Ca（OH）2,and waste acid.During the neutralizing reaction,heavy metals deposited in the process of hydrolyzation and arsenic was mainly removed by the formation of arsenate and arsenite.After the neutralizing reaction at pH of 12.4,the concentration of harmful elements decreased from 103—102 mg/L to around 1mg/L.The successive processes including addition of flocculation,solid-liquid separation via concentration and air oxidation further lowered the concentration of the harmful elements to around 10 2 mg/L,lower than national standard（GB 4913— 85）.The weight loss of the sludge increased with the increasing of the reaction temperature.Free water and crystal water were sequentially removed in the range of room temperature to 160 ℃;arsenic oxides began to volatilize at the temperature around 400 ℃;when the temperature increased to the range of 600—800 ℃,a small amount of CaCO 3 in the sludge decomposed to CaO;at the temperature above 1050 ℃,the main phase of CaSO 4 began to decompose to CaO followed by an obvious weight loss.The contents of As and Se in the sludge leaching solution in the toxic leaching experiment were obviously higher than national standards（GB 5085.3—2007）,indicating that this sludge was a hazardous waste.