Purification of circulating and waste water in metallurgical industry using complex coagulants

Abstract

The main goal of waste water treatment of metallurgical production is to return water to the circulating water supply system. The main pollutant of most process effluents are suspended substances, or suspensions. The key parameter for evaluating the cleaning efficiency is the residual content of suspended substances, which should not exceed 1–10 mg/l, depending on the technological purpose of the water. The most promising reagents for physic-chemical water treatment are complex coagulants that combine salts of two or more metals. Such reagents are free from the disadvantages of traditional coagulants, and large-scale wastes from various industries can be used as raw materials for their production. Complex coagulants based on aluminum salts, when aluminium is modified by the products of hydrolysis of titanium compounds, have proven to be highly effective in treatment processes of waste water of various origins. Testing of the complex coagulant obtained in the process of modifying of traditional aluminum sulfate by the products of hydrolysis of titanium compounds was carried out on waste water from gas cleaning plants for coal preparation, coking plants and electric arc furnaces for steelmaking. In terms of its effectiveness, the complex coagulant exceeded traditional aluminum sulfate and was as close as possible to the more expensive and modern aluminum oxychloride. The increased efficiency of the complex coagulant is due to flocculation and nucleation phenomena occurring on the surface of titanium compounds compared with aluminum sulfate. The complex coagulant was less sensitive to fluctuations in the pH of the treated water than pure aluminum sulfate. As a result of water treatment, it was possible to achieve a reduction in the content of suspended substances below 1 mg/l, which will positively affect the economy of the water treatment process. The rate of flake deposition and filtration of treated water, using complex coagulant, significantly exceeded both samples of the most common coagulants. Increased sediment density will reduce reagent costs for its dehydration, as well as the area required for its placement.