| China is a big country of a long history of coal production. In the selection process of coal mining will produce a large amount of coal gangue. Coal gangue idle accumulation not only takes up a lot of land, but also is a waste of resources, causing serious impact to the environment and ecology. Therefore, treatment, disposal and resource utilization of coal gangue research has become imperative.Inorganic polymer flocculant is a new type of water treatment agent,developed on the basis of traditional aluminum salt and ferric salt which have more excellent performance on the treatment containing fine particles in the wastewater than traditional flocculant, and more cheaper than organic polymer flocculant. Coal gangue is mainly composed of SiO2, Al2O3, Fe2O3 and CaO components of the total content, usually in more than 95%, which is rich in the main ingredients for preparing aluminum inorganic polymer flocculant, natural raw materials for preparation of inorganic polymer flocculant. If the energy of coal gangue in aluminum, iron, calcium utilization, looking for synthetic route suitable, preparation of inorganic polymer composite flocculants aluminum, iron, calcium, and through theoretical research to reveal the mechanism of synergistic effect of aluminum, iron, calcium flocculant, has important theoretical and practical significance for the comprehensive utilization of coal gangue. This paper is studied on using coal gangue through calcined, acid dissolutionand alkalization polymerization process, preparing a new type of high efficient inorganic polymer flocculant - polymeric ferric aluminum calcium chloride (PAFCC). Focus on the preparation process of calcination, acid soluble, alkaline polymerization process factors influence on the stage of product, production process was optimized by orthogonal experiment. At the same time, the structure of the product was characterized by using modern analysis and testing means, and studied the performance of mechanism and application.Through the comparative analysis before and after calcination, calcination plays an important role in the formation of high efficient PAFCC. The main mineral of coal gangue is kaolinite (Al2O3·2SiO2·2H2O), which is composed of a layer of silicon oxygen tetrahedron and a layer of aluminum oxide eight surface body type 1:1 layered silicate clay minerals, the coordination number of Si and Al were 4 and 6. Structure of single layer completely the same, the interlayer is connected by hydrogen bonding, anhydrous molecules and ions, by a common oxygen atom connected together to form cell. Cell coupling between closely, not easy to disperse. Coal gangue calcined in loose state, crystalline nodes in the burning process of dehydroxylation of kaolinite due into amorphous metakaolin (Al2O3·2SiO2),metakaolin have large surface area and high chemical reactivity, the decomposition of SiO2,Al2O3 had higher soluble.The calcination temperature is below 600℃,calcined coal gangue removing structure for water residue and kaolinite in coal combustion,coal gangue in carbon difficult to remove completely;When temperature is higher than 950℃,metakaolin has been completely destroyed, coal gangue will form a new spinel phase and lose activity. The best calcined temperature is 750℃.In this temperature, the effective substances has high dissolution rate and the highest activity of coal gangue.Through the chemical analysis,in coal gangue,SiO2, Al2O3 and Fe2O3 contents were 52.15%,22.67% and 4.01%,respetively. The content of Al2O3 is more abundant, which used for the preparation of poly aluminum chloride water treatment agent is feasible. The results showed that coal gangue stone crushing to 0.2mm, calcination temperature of 750℃,natural cooling, at atmospheric pressure, reaction temperature is 105-108℃ (azeotropic temperature water and hydrochloric acid),20%(mass fraction) of hydrochloric acid leaching reaction condition optimization from coal gangue effective substances:acid leaching time 3H,The acid 0.7g/g, ratio of solid to liquid 1:4, aluminum, iron, calcium dissolution rate are respectively 53.7%,6.08%,2.56%; alkaline polymerization stage optimal reaction condition is:the polymerization time 30min, temperature 60℃, pH value of 3.7, the product of salinity is 60.3%. The prepared product conforms to our country of poly aluminum chloride (PAC) national standards (GB15892-2009), able to market.After an analysis of modern testing instruments.PAFCC is a kind of ettringite 3CaO·Al2O3·3CaSO4·31H2O and iron aluminate C2AxF1-x (x=0-0.67) structure of the material, a hollow tube columnar crystal shape structure; vibration peak frequency anions vibration peak frequency, hydroxyl and water main features spectrum in PAFCC and eight hedron cation and interlayer cations of Ca2+ vibration peak frequency, the presence of Al-O-H-Al and Fe-O-H-Fe in the molecular structure, is a chlorinated aluminum, iron multi hydroxyl polymer. PAFCC is a good ordering monoclinic substances, speculated that the general molecular formula: [Al(13-x-y)FexCa2NaSiyO22(OH)z]mCl(24-z)·nH2O,0≤x≤5,0≤y≤8,0≤z≤24.The coagulation test of coagulation characteristics of the prepared PAFCC and PAC were studied respectively. The results show that PAFCC flocculant on the optimization conditions of kaolin wastewater treatment:dosage of 500mg/L, the pH value of the wastewater is 8, the settling time is 15min, the stirring speed is 200r/min; PAC flocculant on the optimization conditions of kaolin wastewater treatment:dosage of 500mg/L, the pH value of the wastewater was 9, settling time for 15min, stirring speed of 200r/min. Under their optimum conditions of kaolin processing wastewater, PAFCC wastewater treatment PAC is better than the treatment effect of the sludge dewatering, filtering performance is better than that of PAC. PAFCC flocculant has a strong flocculation and adsorption bridging ability; in the flocculation separation process, not only the electrical neutralization, the compression of electric double layer effect, impurity particles and formed during the hydrolysis process of multi-core hydroxyl complexes of water can strongly adsorb;coagulation flocculation mechanism of PAFCC is the surface complexation and surface the precipitation process. PAFCC due to the existence of Ca2+reaction system, by neutralizing the negative charge effect of colloid, and effectively exert the coagulation aid, while reducing the charge density of the colloidal particles, the viscosity[η] of the sludge characteristics are improved effectively, improve the permeability coefficient of the sludge, improve the sludge dewatering performance. |
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