Investigation On Arsenic Recovery And Value-added Utilization From Arsenic Waste Water

With the metallurgical and chemical industry development, arsenic-containing waste water untreated, directly into the natural water may seriously pollute the environment and affect our everyday lives. However, at present, decontaminate treatment is the only way to deal with the waste water, and recycling of the useful element has not being extensively investigated. As for the economic and ecology sustainable development, it is very important to explore an economical and technological process to recycle the useful element, as well as to protect the environment and bring economic benefits. This work, intended to develop a new environmental protective process to recycle the arsenic, lessen its pollution and realize comprehensive utilization, has theoretical and practical sense.This paper, taking the acidic arsenic metallurgy waste water as the research object, crystallization of sodium arsenate in its solution after alkali leaching was studied. The affect of temperature, time, and the mixing speed on the crystallization was investigated. Through three-factor three-level orthogonal experiment, the parameters were optimized. Sodium arsenate as raw material, hydrazine hydrate as deoxidizer, the affect of hydrazine hydrate dilution times of, pH value, hydrazine hydrate excessive coefficient, temperature, and strength of ultrasonic on first arsenic recovery rate is discussed. Based on the single factor orthogonal experiment, process parameters of arsenic preparation through reduction of sodium arsenate were optimized. Under best conditions, the kinetic process of arsenic preparation through reduction by hydrazine hydrate is studied. The conclusions were as followings:(1) The best process parameters of sodium arsenate crystallization were: Crystallization temperature:30℃; Crystallization time:45min; Mixing speed:300 rpm(2) pH value, temperature, hydrazine hydrate excessive coefficient and ultrasonic strength affected a lot on the first arsenic recovery rate. Under ultrasonic condition, arsenic recovery rate first increased then decreased with pH increasing, and the maximum rate is reached when pH is7. Ultrasonic had an important impact on the arsenic recovery rate and the best recovery rate is obtained when ultrasonic strength is160W. The recovery rate varied a lot when temperature changed. Before70℃, arsenic recovery rate increased with temperature increasing, but did not continue to increase when it passed70℃. The larger hydrazine hydrate excessive coefficient is, the better arsenic recovery rate, but, on account of the cost, it is better to make the excess coefficient at2. Other terms rarely affected the recovery rate.(3) The best parameters of sodium arsenate deoxidization under ultrasonic condition were:pH:7; Hydrazine hydrate excessive coefficient:2; Dilution times:5; Ultrasonic strength:160W; Temperature:70℃.Under the best parameters, the first arsenic recovery rate is62.91%.The second recovery rate is91.77%.(4) The order to arsenic deoxidization by hydrazine hydrate is1.92, Kinetic equation is: or Relationship between k and T: the apparent activation energy: Pre-exponential factor:...