Study On Extraction Technology And Mechanism Of Acid Leaching Of Gangue

Coal gangue is an industrial solid waste in coal mined, washed and processing produced, it accounts for about 15% to 20% of coal production. Coal gangue contains large amounts of silicon, aluminum, iron, titanium and other minerals. We research on the extraction, separation of these valuable substances and thus the production of high value-added processing of silicon, aluminum, iron, titanium-based chemical products. So, according to our researched, not only can solve gangue lot of land, pollution of the environment, easy to geological disasters occur, but also to solve the shortage of resources of other issues. Therefore, the study of coal gangue comprehensive utilization of resources is an important way to build a resource-saving society; it has a very important practical significance to promote the China’s sustainable development strategy.Since the 1950s, people had begun research on the utilization of coal gangue. Currently, the ways of coal gangue’s use are:use as a fuel, the production of building materials, land reclamation, subgrade materials. However, the mentioned utilization of coal gangue belong to the extensive use of direct used, failed to give full play to the potential value of coal gangue, greatly reducing the added value of gangue.In this study, taking coal gangue from Panxian of Guizhou as the research objects. By making use of mechanical activation of coal gangue, it has some activity, and then coal gangue with different concentrations of the sulfuric acid was neutralized, leaching reaction, extracted coal gangue valuable elements, and thus the preparation of chemical products. Research shows:(1) Mechanical activation makes gangue reactivity increase, creating favorable conditions for the extraction of coal gangue in the valuable elements.(2) The gangue material is a typical low calorie, the high iron and high titanium content coal gangue. In the sample, SiO2 content accounted for 37.29%, Al2O3 accounted for 17.35%, Fe2O3 accounted for 18.19%, TiO2 accounted for 3.95%. Sample phase composed mainly of kaolinite, quartz, carbonates, anatase titanium oxide and hematite, siderite, and so on.(3) Study examined the effects of acid concentration, reaction time, bath temperature, and liquid-solid ratio on the iron removal and titanium enrichment, and the orthogonal experimental design is based on the single factor experiments to optimize the process conditions of iron removal and titanium enrichment. The experimental results showed that:the iron removal and titanium enrichment optimum conditions are acid concentration of 10%, reaction temperature 60℃, reaction time 3h, liquid-solid ratio 6:1. Under these conditions, the rate iron removal reached 89.01%, the rate titanium enrichment reached 42.93%. The kinetic equation of the neutral reactions of deiron is1-2/3x-(1-x)2/3=2/3kt. The apparent activation energy for the neutral reactions of deiron is 19.58kJ/mol. In the neutral reactions of coal gangue, the reaction kinetics model belongs to the solid membrane diffusion control of unreacted shrinking core model of grain diameter narrowing shrinking core model.(4) Study examined the effects of acid-residue ratio, reaction time, and reaction temperature on the leaching reaction and the orthogonal experimental design is based on the single factor experiments to optimize the process conditions. The experimental results showed that:acid-residue ratio 1.4, reaction time 4h, and reaction temperature 170℃. Under these conditions, the leaching rate aluminum, iron and titanium reached 97.47%,89.69% and 92.11%, respectively. Acid leaching of aluminum leaching kinetics equation can be used to describe 1-(1-x)1/3kt, the apparent activation energy of the reaction 61.32kJ/mol. In the acid leaching reaction of the neutral residues of coal gangue, the reaction kinetics model belongs to the interface chemical reaction control of unreacted shrinking core model of particle unchanged shrinking core model.(5) Study examined the effects of the dissolution time, dissolution temperature, and dissolution liquid to solid ratio, dissolution liquid acid concentration on the dissolving reaction and the orthogonal experimental design is based on the single factor experiments to optimize the process conditions. The experimental results showed that:dissolution time 60min, dissolution temperature 80℃, dissolution liquid acid concentration 5.0%, dissolution liquid to solid ratio of 5:1. Under these conditions, the leaching rate aluminum, iron and titanium reached 98.44%,90.49% and 93.11%, respectively. The dissolution process kinetics model belongs to liquid boundary layer diffusion controlled.(6) The phase and micro-morphology of the coal gangue, the neutral residues, the acid leaching undissolved materials and the acid leaching residues were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS). The results show that:after neutral and acid leaching reaction, the acid leaching residues only have SiO2 and a small amount of CaSO4; it demonstrates aluminum, iron and titanium of can be totally extracted by neutral and acid leaching reaction.This technique in the comprehensive utilization of coal gangue can be reached higher valuable elements extraction rate, and acid leaching residue has the silicon content highly and impurity content lowly, and it can provide a better recycling foundation of the acid leaching residue. At the same time, this technique provides a theoretical basis and experimental guarantee for coal gangue resources comprehensive utilization and industrial production expanded test. This study will have good social, economic benefits and important practical application value. It has important significance for the efficient resource comprehensive utilization of the coal gangue.