Study On The Synthesis Conditions Of Calcium Carbonate With Various Morphologies From Calcium Carbide Slag

In this dissertation,calcium ion(Ca²⁺)was leached by ammonia chloride from calcium carbide slag and subsequently converted into dendritic,cubic calcium carbonate（Ca CO₃）and Ca CO₃ whiskers via replacement reactions or CO₂carbonization method,and the detailed synthetic conditions of Ca CO₃ crystals with various morphologies were studied and determined.The main work and summary are as follows:（1）Preparation of dendritic calcium carbonate from calcium carbide slagUsing calcium carbide slag as the calcium source,NH₄Cl as the leaching agent,and Na₂CO₃ as the carbonization precipitating agent,ethylene glycol was selected as the most suitable crystal form control agent and the suitable synthetic process conditions for the dendritic calcium carbonate were investigated and determined as follows:The addition of alcohol added 3%,reaction temperature 80℃,the initial concentration of Ca²⁺0.5 mol·L^-1,reaction time 30 min,and the molar ratio of Ca²⁺to CO₃^2?1:0.8.The sample prepared under this condition is a mixed phase of aragonite and calcite,which is formed by Ca CO₃ dendrites with a length of about 2μm and a diameter of about 200 nm.The regularity of dendritic Ca CO₃ sample was positively correlated with the content of aragonite in the sample.（2）Preparation of cubic calcium carbonate from calcium carbide slagUsing calcium carbide slag as the calcium source,NH₄Cl as the leaching agent,and NH₄HCO₃ as the carbonization precipitating agent,the Mg（OH）₂ was selected as a more suitable crystal form control agent to prepare the cubic crystalline Ca CO₃,and the suitable synthetic process conditions for the cubic calcium carbonate were investigated and determined as follows:The addition of Mg（OH）₂ 5%,reaction temperature 40℃,the initial concentration of Ca²⁺0.5 mol·L^-1,the stirring speed 400rpm,reaction time 20 min,the molar ratio of Ca²⁺to HCO₃^?1:1.The calcium carbonate sample prepared under this condition shows regular cubic particles and good distribution,with uniform particle size of about 3μm.（3）Preparation of calcium carbonate whiskers from calcium carbide slagUsing calcium carbide slag as the calcium source,NH₄Cl as the leaching agent,and CO₂ as the carbonization precipitant,sieving and determining Mg Cl₂ was selected as the more suitable crystal form control agent for the calcium carbonate whiskers,and the suitable synthetic process conditions for the calcium carbonate whisker were investigated and determined as follows:The addition of Mg Cl₂ 5%,the initial concentration of Ca²⁺0.4 mol·L^-1,reaction temperature 80℃,the stirring speed 200rpm,the CO₂ flow rate 180 m L·min^-1.The calcium carbonate whisker sample prepared under this condition performs regular morphology and uniform particle size distribution,with the aspect ratio of about 30（length of about 6μm and diameter of about 200 nm）.