Study On Carbon Dioxide Mineralized Curing Light Weight Aggregate Made Of Solid Waste And Heavy Metal Precipitation Of The Aggregate

The emission of carbon dioxide and other greenhouse gases has caused a lot of environmental problems.While carbon dioxide mineralization curing building materials technology has huge carbon sequestration potential,it can effectively improve the performance of building materials,reduce the high energy consumption brought by the traditional curing process,shorten the curing cycle of building materials and absorb a large amount of industrial solid waste,with good environmental and economic benefits.At present,our country is gradually limiting the mining of natural sandstone aggregate and gradually shut down mining aggregate,which brings vast market for artificial aggregate.Traditional sintered aggregate has high energy consumption,and using clay as raw material,which is a non-renewable resource,has been gradually eliminated.The steam cultured aggregate also has the problems of high density and low strength.At the same time,high temperature steam curing is required and the energy consumption is high.At the same time,solid waste contains a certain amount of heavy metal elements,with which to prepare building materials,the problem of heavy metal precipitation also needs to be considered.Aiming at the problems of high density,low strength and high energy consumption of steam-fed aggregate and heavy metal precipitation of solid waste,this paper selects blast furnace slag and fly ash as raw materials,studies the formulation optimization,curing system,the influence of alkali activator and the characteristics of heavy metal precipitation of carbon dioxide mineralization curing lightweight aggregate,and prepares a kind of solid waste lightweight aggregate that meets the national high strength lightweight aggregate standard.The main work is as follows:Aiming at the problems of high density and low strength of traditional aggregate,this paper systematically studied the influence of fly ash slag mixing ratio and carbon dioxide mineralization curing conditions on the strength and carbon sequestration rate bulk density,clarified the kinetic principle of carbon dioxide mineralization reaction and the mechanism of mineralization reaction affecting the strength,and realized the strength improvement and density reduction.After optimization,the mixture of 40%blast furnace slag and 60% fly ash was used as the main raw material for the preparation of lightweight aggregate.The research shows that under the condition of unchanged raw materials,the carbon fixation rate is controlled by carbon dioxide diffusion,while the strength is influenced by hydration products and mineralization products.Finally,the curing system of 0.1MPa curing pressure,0.2 remaining water solid ratio,3 days pre-curing time and 2h mineralization curing time is optimized.Under this condition,the compression strength of the lightweight aggregate cylinder is increased by 20%compared with the natural curing,which can reach 3.6MPa,but it still does not meet the requirements of the national standard.Aiming at the problem of low strength after optimizing the ratio of solid waste and curing process,this paper systematically studied the influences of sodium hydroxide,calcium hydroxide and sodium silicate on the crystalline phase composition,pore structure,cylinder pressure strength and carbon fixation rate of the system,and clarified the mechanism of alkali excitation and its influence on mineralization reaction.After adding alkali activator,the strength was greatly improved,reaching the national standard.Requirements for high strength lightweight aggregate.The experimental results show that sodium silicate has the best alkali excitation effect on natural curing samples,but excessive sodium silicate will inhibit the hydration reaction of samples.At the same time,the adaptability of sodium silicate to the mineralization reaction is very poor.The strength of the samples with sodium silicate is decreased after the mineralization reaction.However,calcium hydroxide has good adaptability to mineralization reaction.When the content is 5%,the strength after mineralization curing exceeds 7MPa,which is far higher than the national standard for high strength lightweight aggregate of 6.5MPa.Although sodium hydroxide performs well under natural curing and mineralization curing,its strength enhancement effect is not as good as calcium hydroxide because there is no calcium component supplemented by calcium hydroxide.Aiming at the problem of heavy metal precipitation caused by solid waste preparation of building materials,this paper studied the main existing forms of copper,lead,chromium,cadmium and zinc in the system before and after the mineralization reaction,as well as the amount of precipitation under different working conditions.The results show that most heavy metals(copper,zinc,chromium,lead)have a high amount of precipitation under natural conservation,and the precipitation of heavy metals is mainly controlled by diffusion.The mineralization reaction can effectively inhibit the diffusion of ions in the system and reduce the precipitation of heavy metals.However,the precipitation amount of cadmium is very low under natural curing,which is mainly controlled by the dissolution amount of heavy metal elements in pore water.After the mineralization reaction,the precipitation amount increases,so the solid waste with high cadmium content is not suitable for the mineralization curing process.