Abstract: Calcium in waste calcium carbide residue was extracted with aqueous NH₄Cl solution,the obtained solution was purified simultaneously and high purity calcium carbonate was prepared by introducing CO₂.Effects of aqueous NH₄Cl solution concentration,excessive extent,and reaction temperature etc.on Ca extraction and purification were investigated.When aqueous NH₄Cl solution concentration was at 3%~27.11% and NH₄Cl excessive extent was at 0~25%,the removal rate of impurity Mg was increased with the increasing of aqueous NH₄Cl solution concentration,and was slightly increased with increasing of excessive extent;and the extraction rate of Ca was hardly affected.At 15~70 ℃,the leaching temperature hardly improved the extraction rate of Ca,but Mg removal rate was slightly lowered with the temperature rising.Optimum operation conditions to extract and purify Ca were as follows:aqueous NH₄Cl solution concentration was 10% (mass fraction),NH₄Cl excessive extent 10%,room temperature,and reaction time was 60 min.Adjust pH of CaCl₂ solution to 12.00 with aqueous ammonia solution,and react with CO₂,the purity of the obtained CaCO₃ was 99.44%,white content was 97.8%,impurity Mg content was 0.015%,and particle size was 500 nm.

Key words: calcium carbide residue, ammonium chloride, calcium carbonate