| Calcium hydroxide is the main component of calcium carbide slag,which is partially converted into calcium carbonate due to long-term open storage.In addition,there are a considerable amount of impurities,such as magnesium hydroxide,iron aluminum oxide,acid insoluble substance,sulfide,phosphide,etc.Calcium in calcium carbide slag is converted into calcium oxide to remove impurities and obtain high purity refined calcium carbide lime.After mixing with ordinary calcium carbide slag to meet the quality requirements of calcium carbide production,a recycling process is formed,which is an effective way and method to solve a large number of solid waste of calcium carbide slag in PVC industry.The content of related components of calcium carbide slag was studied,including chemical components and mineral components.The results showed that the total calcium oxide content was 86-87%,while the effective calcium oxide content was low,80-83%,magnesium content was about 5-6%,followed by iron aluminum oxide,which was about 3-4%.In addition,there was a certain amount of acid insoluble,which was 1-2%.Firstly,the acid-soluble impurity removal method was considered.The dilute sulfuric acid was directly reacted with the electroslag,and the main components reacted to form calcium sulfate solid,while other impurities produced liquid soluble products for filtration and removal.The optimum technological conditions of acid dissolving method are as follows:the solid content of the slurry of calcium carbide slag is 250 g/L,the concentration of sulfuric acid added to the slurry is 1 mol/l,the pH of the reaction mixture is 4-5,and the reaction process lasts for 3 hours.The reaction mechanism of acid dissolving method was explored.The reaction models of sulfuric acid and calcium carbide slag were calculated from reaction kinetics and thermodynamics.It is found that the whole reaction process is mainly controlled by internal diffusion in the first few seconds,while it is.controlled by interfacial chemical reaction in the last few seconds.The mechanism of enhanced reaction was analyzed qualitatively.The reaction process was enhanced by high-speed dispersion homogenizer and the raw materials were ground to obtain calcium sulfate with better purity.The final product of high purity calcium oxide was obtained by reducing thermal decomposition of the intermediate of high purity calcium sulfate,and the effective calcium oxide content was 96-97%.Continue to study the ammonium salt leaching method,to explore the effect of leaching impurity removal,to obtain the best process conditions.The optimum conditions of(NH4)2SO4 leaching were as follows:the concentration of(NH4)2SO4 solution was 40 g/L,the excess of(NH4)2SO4 was 40%,and the reaction time was 90 min at 80℃;the optimum experimental conditions of NH4Cl leaching were as follows:the concentration of NH4Cl leaching solution was 120 g/L,at room temperature,the reaction time was 40 min,the excess of NH4Cl was 10%.By refining calcium carbide slag,compared with the ordinary calcination process,high purity calcium oxide product was obtained.Using sulfuric acid to dissolve calcium carbide slag and remove most impurities,the final purity of calcium oxide is 96～97%.The technology of acid dissolving and impurity removing combined with gypsum acid making is simple and mature.Under the idea of proportioning and mixing,the investment and operation cost is low.Although the leaching method has better impurity removal effect,the purity of the product is 98～99%,but the process is more complex and the cost is higher.Generally speaking,the acid dissolution method is the most ideal method for the resource recovery and utilization of calcium carbide slag. |
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