Formation,Evolution And Functional Regulation Of Phlogopite Vermiculite In The Vermiculite Deposit,Yuli,Xinjiang

Vermiculite is a layered silicate mineral with TOT type layered structure.Most natural vermiculite is formed by weathering of phlogopite.Due to incomplete weathering,the vermiculite mined is usually phlogopite vermiculite interlayer mineral.The vermiculite produced is also phlogopite,the ratio of interlayer to vermiculite is variable,and the iron content is not uniform.At the same time of mining vermiculite,a large amount of phlogopite is also mined out.Because of weathering,this part of phlogopite has high purity.However,due to its completely different physical and chemical properties from vermiculite,it can not be effectively used as vermiculite.It is often stacked in tailings dam or sold at a very low price,resulting in a waste of resources,if we can use mineral processing method to process this part of difficult to use phlogopite,it can greatly improve the economic value while processing tailings.Based on the study of the formation and evolution of vermiculite in qieganbulake vermiculite deposit in Yuli,Xinjiang,the physicochemical conditions for the transformation of phlogopite into vermiculite are obtained.In addition,the phlogopite in the ore deposit is used as raw material to transform the phlogopite which can not be used efficiently in the tailings dam into phlogopite vermiculite interlayer mineral or vermiculite by hydrothermal synthesis under laboratory conditions.Based on the successful transformation,the effects of temperature,K⁺concentration,pH value and hydrothermal time on the products were studied.Use modern analysis and determination methods,such as X-ray powder diffraction(XRD),X-ray fluorescence spectroscopy(XRF),inductively coupled plasma emission spectroscopy(ICP),and transmission electron microscopy(TEM),are used to analyze the phase,chemical component,crystal structure,and microstructure of the product before,during,and after transformation.Results indicate that phlogopite can be transformed into vermiculite in Mg Cl₂or Na Cl solutions under acidic hydrothermal conditions;in addition,the transformation rate increases with temperature.To promote transformation,the solution is changed during transformation to remove K⁺,Thus,the chemical equilibrium in the conversion reaction can be changed so that more K⁺can be exchanged.The transformation effect under weak acid conditions is higher than that under neutral or alkaline conditions.During transformation,K⁺is leached from the interlayer,whereas phlogopite is first transformed into a phlogopite-vermiculite mixed layer(i.e.the phlogopite layers is the most),and then into a vermiculite-phlogopite mixed layer(i.e.the vermiculite layers is the most),and finally completely into vermiculite.At the same time,the preparation experiments of expanded vermiculite were carried out.On the basis of previous studies,the effects of composition,the amount of expansion agent(oxalic acid dihydrate and hydrogen peroxide)and pre expansion time on the final expansion effect of expanded vermiculite were studied.The results were analyzed by field emission scanning electron microscope(SEM).The results show that the closer the composition of expanded sample is to that of pure vermiculite,the better the expansion effect is;when the ratio of oxalic acid dihydrate to hydrogen peroxide is 0.14g:1.5m L,the best expansion effect is obtained;the expansion effect is basically unchanged when the expansion agent is added continuously;the better expansion effect is obtained after extending the pre expansion time for 24h.Finally,the adsorption experiments of Pb²⁺containing wastewater were carried out by using the synthesized expanded vermiculite.The influence of different particle size,time and pH on the adsorption results was studied,and the maximum adsorption capacity was tested.The results show that the expanded vermiculite with 100 mesh size has a good adsorption effect on Pb²⁺in the wastewater under normal temperature and can reach the adsorption equilibrium within 30 minutes.The maximum adsorption capacity of Pb²⁺in wastewater was186.332mg/g,and the adsorption process was fitted by the second-order rate equation.Compared with all kinds of vermiculite adsorption materials in recent years,it has certain advantages in terms of adsorption equilibrium time and adsorption capacity.These results are valuable for the study of the crystal structure and origin of vermiculite,as well as the synthesis and application of vermiculite.