Carbon emission reduction potential and life cycle assessment of calcium carbon slag utilisation
Recycling of calcium carbide slag in areas such as building materials,environmental treatment and chemical products can realize the utilization of industrial waste slag and carbon dioxide emission reduction.Under the dual-carbon background,it is particularly important to analyse the carbon reduction potential of calcium carbide slag in terms of carbon sequestration and its recycling pathway.The particle size distribution and chemical composition of calcium carbide slag in the representative production areas were counted in detail,the theoretical carbon sequestration was calculated based on the calcium oxide content in each slag,the carbon emission reduction effect of various recycling pathways of calcium carbide slag was analysed systematically as well as the specific implementation steps in the life-cycle assessment(LCA),and the application cases of LCA in the field of calcium carbide slag were introduced.The calculation results show that the theoretical carbon sequestration of calcium oxide is positively correlated with the content of calcium oxide of calcium carbide slag.The calcium oxide mass fraction of calcium oxide in calcium carbide slag from Xinjiang and Hebei are both about 90％,and the calcium oxide mass fraction of calcium carbide slag from Shandong is lower,about 61％,and the theoretical carbon sequestration of calcium car-bide slag from six origins,including Shandong and Xinjiang,floats in the range of 0.48 to 0.72 t/t(electrochemical slag).In the field of calcium carbide slag recycling,calcium carbide slag,whether it is a substitute for limestone raw materials for the production of cement,bricklaying,calcium chloride and calcium carbonate and other construction and chemical products,or its alkaline characteristics for flue gas desulphurisation and industrial wastewater treatment,according to the respective differences in the scale of the industry can be dif-ferent degrees of reduction of carbon dioxide emissions,to achieve the purpose of carbon emission reduction.Among them,calcium car-bide slag in the field of building materials application is mature,the production scale is large,so the total amount of carbon emissions re-duction is larger,on behalf of the enterprise can reduce carbon dioxide emissions by 10 000 t per year on average.Four case analyses using life cycle assessment to calculate carbon emissions from recycling of calcium carbide slag show that 1 t of cement clinker made from calcium carbide slag emits 669 kg of CO2.The CO2 emissions of 1 t of light calcium carbonate made from calcium carbide slag in NH4Cl and(NH4)2SO4 leaching systems are comparable,308.21 and 300.7 kg,respectively,and the CO2 emissions of 1 t of cemented products made from calcium carbide slag are the lowest,about 151.7 kg,and the CO2 emissions of 1 t of cemented products made from calcium carbide slag are the lowest,about 151.7 kg.The lowest carbon emission is about 151.11 kg.It is assumed that the drying pre-treatment process of cement produced by calcium carbide slag consumes a lot of energy,which leads to the high CO2 emission.Com-pared with cemented products,calcium carbonate prepared by calcium carbide slag needs to be added with chemical reagents,such as NH4Cl or(NH4)2SO4,and the indirect emission brought by the increase in the raw and auxiliary materials makes the former's carbon emission greater.The net CO2 emission of calcium carbide slag-cemented products is-301.47 kg/t(cemented products),and the net CO2 emission of calcium carbide slag in NH4Cl and(NH4)2SO4 leaching system to make 1 t light calcium carbonate is-157.5 and-139.3 kg,respectively.It can be seen that calcium carbideslag recycling in the field of cemented products is the best carbon emission reduction.It is suggested that the carbon emission reduction of calcium carbide slag can be studied from this aspect.If the study of carbon emission reduc-tion in the field of calcium carbonate slag cement/calcium carbonate is carried out,it can start from the optimisation of the drying and treatment process of calcium carbonate slag and the addition of raw and auxiliary materials to formulate targeted carbon emission reduction plans.
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