Water Purification from Hydroxo-Compounds of Iron by Ceramic Membranes Based on Clay Minerals

Abstract

The high efficiency of the process of water purification from Fe(III) hydroxo-compounds by microfiltration tubular ceramic membrane based on clay minerals has been shown. This water purification process was developed by Dumanskii Institute of Colloid and Water Chemistry (ICWC), National Academy of Science of Ukraine. The effect of the initial solution concentration, its pH, working pressure, the process duration, and the presence of Cl, SO42− HCO3−, Ca2+ and Na+ ions on the separation properties of membrane was studied. The total salt content of the solution did not exceed the maximum permissible concentration (MPC) of the total mineralization of drinking water. It was established that Fe(III) solutions with Fe(III) initial concentration of up to ∼170 mg/dm3 could be purified to the Fe(III) MPC level in drinking water at pHini 5.0–7.5 and P = 1.0 MPa during the whole process when the membrane specific performance varied in the range 0.28–0.43 m3/(m2·h). As a result of dynamic modification by Fe(III) hydroxo-compounds at the minimum solution pHini 2.8, the membrane retained 33.8% of Ca2+ ions, i.e. acquired the ultrafiltration properties. The presence in solution of Cl−, SO42−, and HCO3− ions, each in the amount of 200 mg/dm3, and Ca2+ and Na+ ions in the amount of 150 and 236 mg/dm3, respectively, practically did not affect the retention of Fe(III) hydroxo-compounds by ceramic membrane. Since such membranes are cheaper than similar membranes based on oxide ceramics and not inferior to them in terms of the efficiency and can work in most severe conditions, they can be used in practice for the purification of the surface and underground natural waters from Fe(III) hydroxo-compounds, including compounds of various classes, such as chloride, sulfate, hydrocarbonate (carbonate), and mixed type. In addition, they can be applied in local installations for pretreatment of drinking water.