Preparation Of Poly Aluminum Ferric Silicate Flocculant From Coal Gangue And Its Application In Chemical Wastewater

Coal gangue is rock trapped in the coal measure strata,and produced in the process of coal mining and washing processing.It has become one of the biggest industrial solid wastes in the annual discharge and accumulative accumulation of stock,which has the hazards of land invasion,environmental pollution and hidden danger of safety.In the process of chemical wastewater purification,flocculation plays a very important role,and polyaluminum-ferric silicate（PAFS）is a kind of commonly used flocculants.The raw material used in this experiment is the coal gangue of Qitaihe mining area in Heilongjiang province,which is rich in Si O₂,Al₂O₃ and Fe₂O₃ components and suitable for the preparation of PAFS flocculant in order to treat chemical wastewater.In this paper,the process of"alkali roasting-acid leaching-polymerization"was used to prepare PAFS flocculant and applied to the treatment of fluoride chemical wastewater.The main research results are as follows:1.Mineral property analysis of coal gangue raw materials show that its microscopic morphology is irregular lamellar structure,and the main components are quartz,cupric alum and kaolinite.The chemical composition of coal gangue is mainly Si O₂,Al₂O₃ and Fe₂O₃,with the contents of 62.883%,23.640%and 4.124%respectively,and has a certain adsorption capacity.The above results show that the coal gangue raw material is suitable for preparing PAFS flocculant.2.PAFS is prepared by"alkali roasting-acid leaching-polymerization"process.The best roasting conditions of the coal gangue modified by Na₂CO₃ were as follows:40%Na₂CO₃content,2 h roasting time,800℃roasting temperature.The best acid leaching conditions were:The acid leaching solid-liquid ratio was 1:6 g/m L,the acid leaching temperature was 60℃,the acid leaching time was 2 h.The optimal polymerization conditions were:p H 3.6,polymerization time 80 min and polymerization temperature 60℃.The turbidity removal rate of fluoride chemical wastewater by PAFS reaches 97.48%under the optimal conditions,the residual turbidity is 16.02 NTU,the basicity of PAFS is 62.16%.PAFS product is light yellow powder.3.The results of thermodynamic calculation and TG analysis show that the solid reaction between Si,Al in the gangue and Na₂CO₃ during roasting process open Al-Si bond,and the reaction of forming soluble silicate and aluminate mainly occurs in the range of 456℃～861℃,and the reaction is the most full at 800℃or greater.4.The results of PAFS characterization showed that PAFS is an amorphous product formed by the complexation of polysilicate acid with Al,Fe and other metal ions.It is a cationic flocculant with a network structure,and has a certain adsorption capacity.The flocculation mechanism of PAFS on fluorine chemical wastewater is electric neutralization,adsorption bridging and net sweep.5.The best flocculation conditions for treating fluorine chemical wastewater by PAFS are as follows:dosage of PAFS is 0.13g,wastewater p H is 10,stirring speed is 300 r/min,stirring time is 3 min,wastewater temperature is 45℃,and settling time is 20 min.Under these conditions,the turbidity removal rate of wastewater reaches 99.80%,and the residual turbidity is1.27 NTU.The flocculation effect is better than the three commercially available flocculants.PAFS is used to treat coomassie brilliant blue dye wastewater,coal chemical wastewater,coal slurry and simulated kaolin wastewater,with turbidity removal rates of 87.34%,95.81%,96.74%and 98.85%respectively.6.The turbidity-time relationship of the sedimentation process of water treatment by PAFS is described using the second-order kinetic model and hyperbolic model.The results show that the correlation coefficients R² of the two models were 0.9585 and 0.9949,respectively.The hyperbolic model could better describe the sedimentation process of treatment of fluorine chemical wastewater by PAFS.The paper has 52 pictures,11 tables,and 93 references.