Research And Optimization Of Preparation Process Of Calcium Carbonate Whiskers

CaCO₃ whisker is an artificially synthesized single crystal material with low cost and wide distribution of raw materials.The crystal structure of CaCO₃ whisker itself is close to the ideal crystal,and mechanical properties such as mechanical strength are also close to that of the single crystal,plus its properties in whiteness,heat resistance,abrasion resistance and other aspects are superior to general materials,thus it has a good application prospect in many fields.The industrialized production of CaCO₃ whiskers is mature in foreign countries such as Japan,US and some European countries,while in China is still immature,and it still stays in the laboratory preparation stage.The key problem is that the prepared whiskers are with low purity and high cost.Therefore,this study mainly aims to solve these problems,so as to produce whiskers with higher purity and more stable parameters in the preparation process of circulating mother liquor.In this thesis,MgCl₂ is used as the morphology controller,and the carbonization method as the most mature method is used to prepare CaCO₃ whiskers.In the laboratory stage,the three-stage process of CaCO₃ whisker growth was first studied,and the important role of Mg²⁺ions in the growth of whiskers was analyzed.It was found that Mg?OH?₂ plays an important role in condensing nuclei,controlling the crystal morphology and improving the purity by reducing the supersaturation of calcium carbonate in the system for the preparation of CaCO₃ whiskers.In addition,this thesis analyzes the growth process of CaCO₃ whiskers to find a process optimization method to improve whisker purity.One method is to increase the relative content of aragonite phase whiskers and increase the purity of whiskers by adding a certain amount of Ca?OH?₂ suspension at the later stage of the reaction to promote the continued growth of aragonite phase whiskers.Specifically,we studied the effect of Ca?OH?₂supplementation on the aspect ratio and purity of CaCO₃ whiskers.Another method is to use a gas disperser to improve the CO₃^2-dispersibility in system.Compared with the traditional tube ventilation,the gas disperser can make the gas enter the system in the form of small bubbles,so that the gas molecules possess a larger liquid-gas interface energy to improve their mass transfer and diffusion,solving the problem of local excessive supersaturation caused by the tube ventilation method,thereby improving the whisker purity.Specifically,the purity of CaCO₃ whiskers prepared with porous stones with different pore sizes was studied.In addition,the mother liquor obtained after carbonization reaction is not an ideal MgCl₂ solution,and there is residue of Ca²⁺and loss of Mg²⁺.Therefore,the mother liquor is titrated with Ca²⁺and Mg²⁺ions and the corresponding supplement is added to achieve the optimal ion concentration,and this method may stabilize the purity of the whiskers prepared by cycling mother liquor.Therefore,the stability of the purity and aspect ratio of the whiskers prepared by recycling the mother liquor have been studied.By adopting the above two process optimization methods,the purity of CaCO₃whiskers is finally increased to more than 99.5%.And the purity of the whiskers prepared by circulating mother liquor is stable,and after 10 cycles of the mother liquor,the purities are also above 99.5%.In addition,based on the optimization results of the laboratory stage,this thesis also scaled up the preparation of CaCO₃ whiskers to the scale of an industrial pilot.The pilot phase circulated the mother liquor to prepare CaCO₃ whiskers,and after 12 cycles,the prepared whiskers are with the purity higher than 96%,the yield greater than 93%,and a stable aspect ratio,which meets market requirements.