Experimental Study On Preparation Of New Coagulant From Coal Gangue And Its Application

Coagulation is the earliest and most commonly used water purification method by human beings.In recent years,the amount of wastewater discharge has been increasing year by year with the rapid development of today’s economy,which means that the demand for coagulants has increased year by year.The production of raw materials such as bauxite and other minerals is decreasing and even depleting.This not only increases the cost of coagulants,but also limits the production of coagulants.Therefore,it is of great significance to seek new cheap raw materials for coagulants.In China,coal occupies a dominant position in energy,and coal gangue has become an industrial waste with the largest discharge and storage capacity,and the weathering of coal gangue during the placement process will produce a large amount of toxic substances and harmful gases,which are harmful to humans and ecology causes great harm.However,the content of Al₂O₃and Fe₂O₃in coal gangue is relatively high.Extracting alumina from it to prepare aluminum and iron products is an important way to utilize coal gangue as a resource.It is of great significance to study the preparation method of using coal gangue to prepare a new type of composite coagulant and its application in water treatment for effectively reducing the amount of coal gangue and achieving low-cost industrial production of coagulant.Titanium salt has the advantages of non-toxicity and good coagulation effect.Titanium-based coagulant using titanium salt as raw material is currently a hotspot of coagulant research.However,common titanium-based coagulants such as Ti Cl₄have certain defects.Titanium ions will rapidly hydrolyze in water,generating a large amount of H⁺,which will lower the pH of the effluent and cause corrosion to metal instruments and pipes.In order to improve the performance of the titanium salt coagulant,various titanium-based coagulants have been developed,but there have been less reports on the use of industrial solid waste gangue to prepare titanium-based coagulants.This topic first prepared inorganic polymer coagulant using coal gangue,and then referring to the preparation principle of inorganic-inorganic composite coagulant,the titanium salt was combined with the inorganic polymer coagulant prepared from coal gangue to prepare polychlorination Calcium aluminum ferric chloride（PAFCC）and polyaluminum iron titanium PTAFC（polyaluminum iron titanium PTAFC）,studied the coagulation reaction of the two coagulants the best synthesis conditions,the best working conditions and reaction mechanism,and finally The actual water has verified the effectiveness of the two coagulants.The main research contents are as follows:（1）Using coal gangue as raw material,high-efficiency inorganic polymer coagulant PAFCC and PTAFC were prepared through high-temperature roasting,acid leaching,titanium doping,polymerization,aging and concentration drying;（2）The effect of acid leaching solution solid ratio,acid concentration,acid leaching time,acid leaching temperature on the dissolution rate of metal ions iron,aluminum and calcium ions in coal gangue was systematically studied.The conditions for the highest dissolution rate of ions are liquid to solid ratio 7:1,hydrochloric acid concentration of 8mol·L^-1,acid leaching temperature of 100℃,and reaction time of 3 hours;（3）The effects of pH,polymerization temperature,polymerization time,curing temperature,curing time on the coagulation performance of PAFCC and the effects of titanium dosage,pH,polymerization temperature,polymerization time on the coagulation performance of PTAFC were systematically studied.The results show that the optimal preparation conditions for PAFCC are:acid leaching solution pH=2,polymerization temperature 60℃,stirring reaction for 5 hours,and aging at 40℃for 28 hours;the optimal preparation conditions for PTAFC are:molar ratio of titanium to titanium 0.3,pH=1.5,polymerization temperature 60℃,polymerization time 3h;PAFCC at the dosage of 110mg·L^-1,pH=9,reaction temperature 20℃,slow stirring speed 40r·min^-1,after standing for 10min The best coagulation effect,the turbidity removal rate reached 98%;PTAFC in the dosage of 70mg·L^-1,pH=7,reaction temperature 20℃,slow stirring speed 40r·min^-1,standing 10min Under coagulation conditions,the turbidity removal rate reaches over 99%,and the residual turbidity is less than 1 NTU;（4）The effect of PAFCC and PTAFC on the removal of turbidity,COD_cr,total phosphorus and ammonia nitrogen in the effluent of secondary sedimentation tanks and refining wastewater of urban sewage treatment plants was studied,and the turbidity,CODcr and color of coal mine water was also studied by PAFCC and PTAFC Degree of removal effect,and compared with commercially available polyaluminium chloride（PAC）.PAFCC and PTAFC have an excellent removal effect on the turbidity and total phosphorus of the effluent and refining wastewater from the secondary settling ponds of urban sewage treatment plants.At the same time,they have a certain removal capacity for COD_crand ammonia nitrogen.Overall,the removal rate of pollutant removal capacity PTAFC>PAFCC>PAC,this may be due to the synergistic effect of Al（Ⅲ）,Fe（Ⅲ）and Ca（Ⅱ）in the PAFCC in the treatment of raw water,which can better play the role of adsorption and neutralization and compression of the electric double layer.There is higher valence Ti（IV）in PTAFC,which can enhance the ability of the coagulant to electrically neutralize and compress the electric double layer,so PTAFC has a higher removal rate of pollutants in water.The research results are of great significance for effectively reducing the amount of coal gangue,widening the utilization of coal gangue,and realizing the low-cost and high-efficiency industrial production and application of coagulant.