Thetechnology And Mechanism Of The Preparation Of Superfine Active Calcium Carbonate By Using Carbide Slag

Carbide slag is the waste residue of the preparation processof acetylene gas from calcium carbide,and it`s main component is calcium hydroxide.The annual output of carbide slag in China is huge,and it is not easy to be treated.It is not only a waste of land,but also causes pollution to the surrounding environment.This paper according to the actual composition of carbide slag from a factory in Shanxi province,preparethe superfine active calcium carbonate products with the reasonable production technology and optimization method.It is not only can obtain economic benefits,but also provide a great way of carbide slag stockpile,easing the pressure on the environment,and has good social benefits.The following are conclusions.1)To explore the way of pretreatment of carbide slag and the best technological conditions,in order to remove the impurities such as iron oxide impurities,and effectively make calcium carbide slag into the form of Ca²⁺.The optimum extraction conditions were as follows:initial preparation concentration of Ca（OH）₂is1mol/L,reaction temperature of 20 degrees C,stirring rate 200r/min,reaction time 20min.Under this condition,we can effectively remove impurities,the conversion rate of leaching Ca²⁺reached 80%.2)Using gas-liquid intermittence carbonization method toprepared light calcium carbonate by using carbide slag.Through the control of different process parameters and reaction conditions,summed up the most superior way of preparation process.The optimal process parameters were as follows:initial preparation concentration of Ca（OH）₂is1mol/L,reaction temperature is 20 degrees C,concentration ofcarbon dioxide is 25%,flow rate is 1.5L/min and stop the reaction when pH of the reaction liquid is reduced to 7.Under the optimal parameters,100g carbide slag material can be prepared toabout 49.3g calcium carbonate particles,particle of the product is cubic block,the median diameter is 6.30μm,d₉₀=14.18μm,surface area is 0.75m²/g.The whiteness of products up to about 95,calcium carbonate 98.4%purity requirements,the above results have reached HG/T2226-2000 quality indicators.3)To explore the different effects of dispersant on the preparation of the superfine calcium carbonate.To further reduce product size,improve the dispersion,to obtain the ideal superfine active calcium carbonate.Selection of calcium carbonate dispersant to optimize the product inquiry,such as triethanolamine,sodium polyacrylate,citric acid,hexametaphosphate sodium,stearic acid sodium and silicone oil and ultimately selected sodium polyacrylate as the optimal admixture,andthe optimal dosage is 2%.Under the optimal conditions,the product results of the particle size test were as follow:the median diameter is 3.22μm,d₉₀=6.46μm,surface area is1.28m²/g.And under the scanning electron microscope and transmission electron microscope（TEM）can be clearly observedthat a great number of calcium carbonate particles which are less than 100 nanometers,except for a small amount of separate existence,a part of attachment formed micron sized aggregates on the surface of the particles,and part to aggregate to form.From the analysis on the mechanism,in the system,sodium polyacrylate mainly in the form of RCOO^-group packages on the surface of the particles that generated from the experiment,and its molecular shows as chain,different chains of molecular adhered on the surface of the particles admixture distal repel each other,which can reduce the surface energy of the grains,block the particles from reunite and continue to grow up,so it can achieve a good dispersion effect,makes the nucleation rate greater than the rate of crystal nucleus growth,finally make the particles present microspheric shape.