This study aimed to investigate the possibility of heat treated diatomite to be used as an adsorbent for chromate removal. In the preparation of heat treated diatomite adsorbent, factor of temperature for calcinations was studied. The optimal condition for adsorption was determined by varying pH, contact time, concentration of chromate, and amount of calcined diatomite at room temperature. The adsorption equilibrium was studied by Langmuir and Freundlich isotherm equations. The interference of competing anions on chromate adsorption was also investigated. The results showed that the heat treated diatomite at 400°C for 6 hour (CD400) was the appropriate adsorbent for chromate removal. By using 1 mg/l of chromate, 8.0 g of CD400, 60 min of contact time, 200 rpm of shaking rate, and pH 6, 42.98% of chromate was removed. The adsorption isotherm of chromate removal was agreed with Langmuir isotherm. Furthermore the adsorption efficiency of chromate was reduced by chloride, nitrate, carbonate, phosphate, and sulphate anions.
