engleski

The effect of initial zinc concentration and coagulant dose on zinc removal from aqueous solutions

The effect of the initial zinc concentration on zinc removal from aqueous solutions by precipitation and coagulation/flocculation has been investigated using the standard JAR test procedure. Precipitation was carried out with milk lime at pH=8.5, and coagulation/flocculation with the FeCl3 coagulant and the commercial organic polymeric coagulants 815C and 130A. The height of the settlement interface has been graphically plotted against settling time, and the settling velocity of the Zn(OH)_2 precipitate has been determined for conditions with and without the addition of various amounts of coagulants. Based on the residual zinc concentration in supernatant solutions and the settling velocity, the zinc removal efficiency has been determined. The results show almost complete zinc removal from all suspensions, but the settling velocity decreases with the increase of the initial zinc concentration. The Kynch and Coa-Clevenger theories have been applied to the calculated values of settling velocity. The total limiting value of mass flux of 0.481 kg/m2h was obtained at initial zinc concentrations of 0.644 g/L. The addition of a coagulant does not significantly increase the mass flux and the settler area remains unchanged when the zinc concentration is below 0.644 g/L. When zinc concentration exceeds this value, the addition of coagulant significantly increases the mass flux and reduces the settler area by two times.

precipitation ; coagulation/flocculation ; zinc removal ; coagulant dose.

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