Titanium-containing coagulants for foundry wastewater treatment

Abstract

Setting up a circulation water supply system is a prerequisite for a modern competitive steel making company. The most frequent problem faced by steel makers includes the challenge of removing suspended solids from large volumes of wastewater. Residual concentration of suspended solids (1-10 mg/l) is the main criterion of treatment efficiency. The most difficult task is to remove particles smaller than 1-2 microns, which stay suspended for a long time. One of the biggest sources of wastewater includes the process of removing residual molding sand from machine parts by water jet surface cleaning. Apart from high concentrations of suspended solids, process wastewater have high concentrations of dissolved organic compounds and require prior treatment before it can go to municipal wastewater treatment plants. Titanium-containing coagulants are being used more and more commonly in water treatment processes due to their high efficiency and the lack of most of the drawbacks inherent in conventional coagulants. This paper compares the conventional coagulants (i.e. aluminum and iron compounds) and coagulants containing titanium salts. In addition, complex titanium-containing coagulants were tested in the actual process of removing residual molding sand from machine parts by water jet surface cleaning. The findings show that titanium tetrachloride outperforms the conventionally used aluminum sulphate and iron chloride, while the effective dose of titanium tetrachloride is on average 2.5 to 3.0 times smaller. The obtained experimental data characterize the effect of added titanium compounds on the water treatment efficiency when conventional reagents are used. It was found that the addition 7.5 wt% of titanium tetrachloride to the conventional aluminum sulphate increases the treatment performance of the latter by 30%. The high efficiency of titanium-containing reagents is due to specific hydrolysis effects, as well as nucleation and flocculation at the surface of hydrolysis products. The rate of sedimentation and filtration of sludges resultant from water treatment with titanium-containing coagulants significantly exceeded that reached when using conventional reagents. The use of titanium-containing reagents will enable to transfer to smaller settlers and filters, reduce the consumption of reagents and reach an enhanced treatment performance. The treated water can be reused or discharged into municipal sewage treatment plants. This research study was carried out as part of the programme supporting research projects carried out by young staff of D. Mendeleev University of Chemical Technology of Russia (Application З-2020-013)