| China is abundant with boron ore resource,most of which distributes centrally in the northeast and western areas of China,such as Liaoning,Jilin,Qinghai and Tibet.Paigeite in Liaoning,which has not been well-utilized due to its complicated mineralogical structure and intricate mineral compositions,accounts for almost 58%of the national boron resources of China.Boron concentrate,one product of magnetic and gravity separation of paigeite,can basically meet the requisite of the boron industry after activated roasting.Nevertheless,most roasting devices in China that used to treat low-grade boron concentrate lag behind,which causes exhaust efflux and low recovery of B2O3.Microwave is a relatively new and clean energy resource.Microwave heating has merits of fast heating,good controllability,high thermal efficiency as well as overall and selective heating,and is able to replace some parts of conventional boron concentrate treating process with high energy consumption and high pollution.In order to solve the problems in roasting and leaching processes of boron concentrate in China nowadays,this paper studied the effects of applying microwave heating in roasting and leaching with boron concentrate instead of traditional heating.Firstly,the influences of roasting temperature,roasting time,microwave power,material amount and particle size of mineral on activation of microwave-roasted products were studied.Furthermore,the reaction mechanism of microwave roast was discussed,and the reaction kinetics model of the leaching process of optimum products of conventional roasting and microwave roasting was established in this research.Secondly,this paper used the Washburn theory and Van Oss-Chaudry-Good equation to study the influence of the microwave field on the surface free energy and its interactions as well as the hydrophilicity of boron concentrate,meanwhile,the effect of microwave on the ?-potential of boron concentrate was studied by the Stern double electrical layer model.Based on research above,the microwave-assisted leaching process of boron concentrate was studied,influences of leaching temperature,microwave power,stirring rate,solid-liquid ratio and material amount on the leaching rate of B2O3 was analyzed.In this study,following conclusions were obtained:1)Microwave energy could fasten the heating rate and increase the activation of boron concentrate.The optimum microwave processing condition is roasting 150g boron concentrate at 600? and 4kW for 10-20 min,in the optimum processing condition,the activation of boron concentrate increased from 64.68%to 86.73%;2)Microwave roasting enhanced both Lifshitz-Van der Waals interaction and Lewis base interaction of boron concentrate surface free energy,meantime,also increased the hydrophilicity of the surface of boron concentrate particles;3)Compared with the traditional roasting,microwave roasting efficiently decreased the}-potential of the boron concentrate.The ?-potential of traditional roasted boron concentrate decreased only about 7.91mV,however,?-potential of microwave-roasted products decreased 15.28mV-17.07mV;4)Extracting the boron component of unroasted boron concentrate by microwave-assisted leaching,the leaching rate of B2O3 increased to 79.63%,which is 14.95%higher than that of conventional leaching process in same leaching condition.Based on characteristics of boron concentrate,this research applied microwave energy on the roasting and leaching process instead of conventional heating sources to shorten the technological process,reduce the processing temperature and time consumption,meanwhile,research also study the non-thermal effect of microwave energy in aspects of the surface prosperities,provides a new approach to efficiently utilize boron component in paigeite as well as a new method to study the functional mechanism of microwave energy. |
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