Water Purification from Zinc Hydroxocomplexes Using Tubular Microfiltration Membranes Made of Natural Materials

摘要

It is shown that tubular microfiltration membranes made of natural materials (ceramics based on clay minerals and lignocellulose derived from wood) that have been developed at Dumansky Institute of Colloid Chemistry and Water Chemistry of the National Academy of Sciences of Ukraine are highly efficient in water purification from zinc hydroxocompounds. The effect of filtration duration, permeate recovery ratio, pH of the feed solution, and the presence of accompanying ions (Cl~-, SO_4~(2-), HCO_3~-, Ca~(2+), and Na~+) on the separation properties of membranes made of natural materials is studied. It is found that these processes can be used at a Zn ion concentration in the feed solution of up to 100 mg/dm~3, which is characteristic of the washing water of electroplating plants; pH 8.5; a total salt content of ＜ 1.0 g/dm~3; P= 1.0 MPa;and η = 80.0%. Under these conditions, the Zn ion concentration in the permeate does not exceed their maximum permissible concentration (MPC) in waste-water. The high rejection ability of the two membranes is associated with the steric mechanism of their action on zinc hydroxocompound particles formed at the given pH_0 value of the solution. The formation of an additional retaining layer of zinc hydroxocompounds in the form of a dynamic membrane on the membrane surface also contributed to the high rejection ability. It is found that accompanying ions adversely affect the rejection ability of the membrane with respect to zinc hydroxocompounds; however, the formation of a dynamic membrane of these compounds counteracts this disadvantage. It is proposed that tubular microfiltration membranes made of clay minerals and lignocellulose should be used for wastewater purification from zinc hydroxocompounds. The precipitate of zinc hydroxocomplexes retained by the membrane, after dehydration in a filter press, can be used in metallurgy as a feedstock for smelting.