Applied Fundamental Research On The Preparation Process Of Ceramsite Using The Acid Leaching Tailings Of Vanadium-bearing Stone Coal Minerals

In China,vanadium-bearing stone coal minerals is a unique vanadium resource,which is rich in reserves.However,due to the low vanadium grade,120-150 tons of vanadium extraction tailings were usually discharged in the production of per ton vanadium pentoxide products.The total amount of vanadium extraction tailings produced by the industry of extracting vanadium from stone coal in China is up to several million tons per year.Sulfuric acid leaching process is one of the main production processes in the current vanadium extraction industry from stone coal in China.The main component of vanadium extraction tailings produced by this process is silicon dioxide,but the sulfate content is relatively high.The industry’s current storage or landfill treatment methods not only cause a certain degree of waste of resources,but also have high environmental risks.It is urgent to develop a new method for resource utilization of acid-leaching tailings of vanadium-bearing stone coal minerals.At present,some studies have shown that the vanadium extraction tailings can be sintered with a certain proportion of aluminum containing auxiliary materials to prepare ceramsite.However,researches on the selection of aluminum containing auxiliary materials and the optimization of process systems are relatively few,and no attention has been paid to the decomposition of sulfates and the release of sulfur-containing components in the vanadium extraction tailings.Therefore,in this thesis,vanadium extraction tailings produced by sulfuric acid baking and leaching of vanadium-bearing stone coal minerals in Northwest and Southwest China were used as raw materials.According to the characteristics of regional resources,suitable aluminum containing auxiliary materials were selected,the process mechanism and main influencing factors were analyzed,the optimized process parameters were determined,and ceramsite products with excellent performance were prepared.The main innovative progress can be summarized as follows:(1)Based on the characteristics of regional resources,a variety of aluminum containing auxiliary materials were selected.Through theoretical analysis and exploratory experiments,one suitable aluminum source was selected as the auxiliary material for vanadium extraction tailings to prepare ceramsite.The optimal proportion between vanadium extraction tailings and the selected auxiliary material was determined,too.In consideration of the composition range of ingredients for firing expandable ceramsite indicated in the Riley phase diagram,as well as the calculation results of the firing coefficients of vanadium extraction tailings and several auxiliary materials,red mud was selected as the auxiliary material for the experimental research of ceramsite preparation.According to the exploratory experiment of preparing expandable ceramsite using mixture of vanadium extraction tailings and red mud with different mass ratios,an optimal mass ratio of vanadium extraction tailings and red mud was determined to be 70:30(2)The preparation process of ceramsite was carried out using the selected materials,and the appropriate process parameters were determined.When the mixture of vanadium extraction tailings and red mud with a mass ratio of 70:30 was used as raw material,the preferred parameters for preparing ceramsite were determined as follows:ramp rate～8 ℃/min,dwell temperature～1080 ℃,dwell time～30 min,and then naturally cooled to room temperature.Ceramsite with a bulk density of 809.3 kg/m3,a water absorption rate of 1.9%and a compressive strength of 9.1 MPa was obtained under this process condition,which can meet the requirements of"Lightweight Aggregate and its Test Methods Part 1:Lightweight Aggregate"(GB/T 17431.1-2010).(3)The expansion mechanism of ceramsite was analyzed according to the morphologies and the crystal phases of ceramsite samples roasted at different temperatures.In the process of preparing ceramsite,the volume of ceramsite shows a rule of firstly shrinking and then expanding with the roasting temperature increases.This phenomenon(the shrinking and expanding)is closely related to the glassy phase produced during the heating process and the gas produced by the release of carbon and sulfur.When the roasting temperature was higher than 1060℃,the amount and viscosity of the glassy phase were large enough.So the SO2 gas released could be encapsulated by the glass phase,and interior pores were formed inside the ceramsite.Consequently,the ceramsite expanded,and its bulk density began to decrease and yielded a minimum value at 1085℃.(4)The release law of sulfur during the preparation of ceramsite using vanadium extraction tailings as raw materials was studied,which can provide some basic data and theoretical basis for using vanadium extraction tailings as one main material to preparing ceramsite with a sulfur content lower than the requirements of lightweight aggregates.Simultaneous thermogravimetric/Fourier transform infrared spectrometry analysis were used to investigate the weight loss,the exothermic/endothermic phenomenon,and the releasing of gases in the process of roasting the vanadium extraction tailings as the raw material for preparing ceramsite.The sulfur contents of samples prepared by roasting vanadium extraction tailings at different temperatures were tested,their crystal phases were characterized,the Gibbs free energies of several reactions were obtained by thermodynamic calculation,and the mechanism of sulfur releasing from vanadium extraction tailings was discussed accordingly.The results showed that the sulfur content(0.44 wt%)of samples obtained at 1200℃ can meet the requirements of lightweight aggregate.Intermediated phases such as Wollastonite(CaSiO3)might be formed by the reaction of Anhydrite and Quartz in the vanadium extraction tailings,accompanied with the releasing of SO2.SiO2,Fe2O3 and Al2O3 in vanadium extraction tailings might be helpful for the releasing of sulfur.