Study On Preparation Of Nano Calcium Carbonate From Marble Polishing Waste

Marble waste deposition not only wastes land resources,but also produces environmental pollution,even threatens people's health and life.In this paper,marble polishing waste was used as raw material,HNO3 was utilized as solvent,and nano-calcium carbonate with uniform particle size distribution was prepared by adjusting the reaction conditions such as the concentration of nitric acid,reaction temperature and time.The technology of comprehensive utilization of waste liquid was also studied.Using Ca?NO3?2 waste liquid as the source of calcium and adding Na2SiO3 solution,chlorine-free hardening accelerator for cement and concrete containing calcium silicate was prepared.At the same time,the hardening accelerator prepared at different conditions were added to paste,mortar and concrete to explore the influence of preparation conditions of hardening accelerator on the properties of cement-based materials.The technological process explored in this article not only makes marble waste effectively treated,but also does not produce waste liquid that causes secondary pollution to the environment.It is a green and environmentally friendly process without secondary pollution.The main conclusions of this article are as follows:Using polishing waste as raw material,the optimal conditions for preparing nano-calcium carbonate are:sodium dodecyl benzene sulfonate?SDBS?as the dispersant,liquid-solid ratio of 10,HNO3 concentration of 1.6 mol/L,reaction temperature at 55?,reaction time was 4 h,and the prepared nano-calcium carbonate have a particle size of about 70 nm,good dispersibility and uniform.The preparation process shows that:the particle size distribution of the raw material is vital to the preparation of nano-calcium carbonate with uniform particle size distribution.The change of the reaction conditions mainly affects the particle size of the calcium carbonate particles and has no obvious effect on the morphology and structure;the steric hindrance effect and electrostatic mutual exclusion effect improve the agglomeration of particles and increase the degree of dispersion of the system.Fixing other parameters and changing the nitric acid concentration to produce Ca?NO3?2waste liquid when preparing nano-calcium carbonate,and using it as the source of calcium,after solid-liquid separation.Adding 0.5 mol/L Na2SiO3 solution to prepare chlorine-free hardening accelerator for cement and concrete.The effects of changing in reaction conditions on the morphology,particle size,and crystallinity of the hardening accelerator for cement and concrete were studied.The study found that the increase of Ca?NO3?2 concentration and reaction temperature led to the decrease of particle size of prepared chlorine-free hardening accelerator for cement and concrete.When reaction time was prolonged,the particle size of the hardening accelerator is reduced,and the morphology gradually changes from accumulated particles to fibrous.When the calcium-silicon molar ratio?Ca/Si?increases,the particle size of hardening accelerator decreases,the degree of polymerization of[SiO4]^4-decreases,and the morphology mainly changes from flaky to short rod-like.The early strength effect of the chlorine-free hardening accelerator for cement and concrete was affected by particle size of the hardening accelerator.The smaller the particle size,the more significant effect.When hardening accelerator prepared at different reaction conditions is added to the paste,mortar and concrete with a content of 3%,the effect of improving the strength has the same regularity.The optimal conditions of preparation hardening accelerator with the best early strength effect are:0.8mol/L Ca?NO3?2 and Na2SiO3 solution are reacted at 75?for 10 h,its 1 d strength increase value of the paste is 125.5%,3 d strength increase value is 54.7%;1 d strength increase value for the mortar is 150.7%,the 3 d strength increase value is 55.8%;the 1d strength increase value for the concrete is 124.6%,and the 3 d strength increase value is 62.6%and does not cause a decrease in the strength of the concrete in the later stage.