Experimental study of wastewater treatment containing sulfuric acid solutions using freezing and thawing method

The aim of this work is to study an industrial wastewater treatment process using freezing. A synthetic solution of water/sulfuric acid was chosen as a simulated wastewater sample. Firstly, the solid-liquid equilibrium of the sulfuric acid/water binary system was studied to determine the range of concentration values and their corresponding temperatures that are suitable for freezing. Secondly, freezing tests were conducted to evaluate the effect of the freezing step on the separation performance of water and acid recovery. The total block flowed by fractionated thawing was shown to be an efficient method that allows a deep purification by a gradient temperature effect, thus removing the solute that incorporates into the ice during the prior freezing step. A statistical model of concentrated sulfuric acid and purified water was developed and used to find the most significant parameters on the process performance. The main parameters studied are the initial sulfuric acid concentration, the freezing temperature, and the thawed ice fraction. The results show that the freezing process performance depends on the concentration of the initial solution and fractionated thawing. However, the freezing temperature did not show any effect neither on the concentrated thawed solutions nor on the purity of the last fraction of melted ice. The higher concentrated fraction of sulfuric acid that could be reached was about 28.9%, it was obtained with an initial sulfuric acid concentration of about 20%. The highest purified fraction was about 0.045%, it was obtained with an initial sulfuric acid concentration of about 0.1%. Generally, the results confirmed the feasibility of the technique and gave a good idea about the operating conditions that can be used for the treatment of wastewater containing sulfuric acid.