Study On COD Reduction For Coal-series Kaolin By Mineral Processing Purification And Low Temperature Roasting And Its Mechanism

Pyrite and carbon materials are always associated in coal series kaolin,which may lead to the COD value being several times higher than that of the market demand.To meet the requirement of filler in glass fiber,etc.the reduction of COD in coal series kaolin through the separation technologies of pyrite and carbon materials,and low temperature roasting has been systematically investigated.The structure,pyrolysis characteristics of carbon materials,and the necessary conditions for thermal decomposition have been revealed.Meanwhile the reaction process and mechanisms of COD reduction were analysed.Moreover the novel technological approaches and theoretical foundation for large-scale comprehensive utilization of coal series kaolin were provided.1.Process mineralogy and COD systematic analysis for coal series kaolinThe coal series kaolin has been characterized by XRF,XRD,FT-IR,TG-DTA and SEM-EDS,etc.The kaolinite accounted for about 85%,and pyrite,anatase took up4%,while the content of non-clay silicate minerals was less in the coal series kaolin.The iron associated in coal series kaolin was mainly concentrated in pyrite,and largely distributed in the size fraction of 60⁷4?m,while the content of kaolinite showed no obvious distinction between different grain size fractions.COD value in coal series kaolin was closely related to the content of pyrite and carbon materials.2.Separation technologies of pyrite and carbon materials in coal series kaolinBased on the conditional experiments of grinding,flotation and high gradient magnetic separation,the process parameters of separation operation were systematicallyinvestigatedandoptimized.Theoptimumconditionsof reverse flotation could be obtained at a grinding fineness of 95.7%less than74?m,sodium hexametaphosphate dosage of 2.0 kg/t at natural pH value,kerosene dosage of200g/t and 2^#frother dosage of 20g/t in decarburization flotation,xanthate dosage of110g/t and 2^#frother dosage of 15g/t in desulfuration flotation.Meanwhile the process parameters of high gradient magnetic separation were magnetic field intensity of 1.2T,pulse rotational speed of 200r/min and slurry flow velocity of 1.0 cm/s.Based on the results from short beneficiation flowsheet,which included one-stage circuit grinding,two-stage flotation and high gradient magnetic separation,the impurities such as pyrite and carbon materials etc.in coal series kaolin have been effectively separated.3.Reduction of COD by low temperature roastingThe COD in coal series kaolin was mainly concentrated in the size fraction of60¹50?m,and the maximum content?27517?g/g?was in 60⁷4?m size fraction.COD value could decrease to 589?g/g at 450?heating-up for 3h and holding for5h.The low temperature roasting was an effective and energy-saving technical approach for COD reduction.The flotation products could effectively enrich pyrite and carbon materials in coal series kaolin,which was extremely important for COD reduction.The COD values of decarburization and desulfuration products were 216202?g/g and200513?g/g.While better results were obtained by roasting flotation concentrate,the COD value could be decreased from 3533?g/g to 2700?g/g at 300?.For stricter demand of COD,the optimum roasting temperature was 400⁴50?,and the COD value of flotation concentrate could be reduced down to 290?g/g.4.Thermal decomposition mechanism and basic theory of COD reductionA linear correlation was observed between COD value and Ea in different grain size fractions.Com₁bined with various integral expressions of mechanism function,??? could be regarded as the most possible mechanism function for the thermal decomposition of coal series kaolin.Based on the theory of principal component analysis,a quantitative description model has been developed for the main influence factors of COD reduction.The accumulative contribution rate of roasting temperature,content of TOC and pyrite has surpassed 96%in the principal components model,which could effectively reflect the influence factors of COD reduction.The molecular structure of carbon materials and oxidation processes of pyrite have been systematically revealed by density functional theory,etc.,so as to provide a theoretical basis for the micromechanism of COD reduction.