Preparation Of Iron Phosphate From Phosphating Slag And Its Application In Biogas Slurry Treatment

Metal parts are often subjected to a phosphating process prior to painting,and phosphating slag is an inevitable product of the phosphating process on the surface of the part.There are many kinds of phosphating slag,among which the zinc phosphating slag contains iron phosphate and zinc phosphate,and a small amount of calcium phosphate.At present,the treatment of phosphate slag in China is in an irregular state,and some small enterprises often adopt direct landfill disposal.Improper treatment of phosphating slag will not only cause serious environmental pollution,but also waste of phosphorus and iron.Biogas digesters have been fully recognized by people for their environmental friendliness,economy,and wide range of raw materials.They are considered to have bright prospects for development and have been widely promoted in rural areas of China.However,the current biogas slurry generated during the biogas production process is difficult to handle.Conventional wastewater treatment methods are not only costly,but the addition of chemical precipitants often causes secondary pollution.In the process of making plywood,a large amount of scrap is often produced.The general treatment method is direct incineration,or a large amount of organic glue is added after pulverization for replasticization,whichever method will cause serious environmental pollution.The phosphating slag is purified to obtain purified iron phosphate and mixed with the scrap of the plywood,pulverized and carbonized to obtain a biogas slurry filter material,and the biogas slurry is filtered.This not only realizes the resource utilization of phosphating slag and scrap,but also reduces the difficulty of biogas slurry treatment,and solves local environmental problems according to local conditions.The phosphating slag was purified three times by hydrothermal pickling,and then calcined to obtain high-purity iron phosphate samples,which were characterized by scanning electron microscopy(SEM)and X-ray diffractometry(XRD).In order to verify the possibility of iron phosphate as a phosphorus source for organic fertilizer,the effects of three low molecular organic acids(formic acid,acetic acid,oxalic acid),mixed acid and sulfuric acid on the release of water-soluble phosphorus in purified iron phosphate were compared.The results show that different low molecular weight organic acids have different ability to release phosphorus for the purification of iron phosphate.The effect ofeach organic acid on the release of phosphorus is as follows: oxalic acid> mixed acid>formic acid acetic acid,in 5g iron phosphate and 500 mL When 10 mmol of oxalic acid was added to the mixed solution of ionized water,the precipitation efficiency of water-soluble total phosphorus was the largest;the phosphorus released from phosphate was mainly related to the acid strength(pH)and complexation of organic acids.The poplar wood chips and the purified phosphating slag are placed in a high-speed pulverizer at a ratio of 1:0,1:0.1,1:0.5,1:1,1:2 for pulverization and mixing,and then at the temperature of 150 ?,250 ?,350 ? and 450 ?is placed in a muffle furnace for carbonization to obtain a final biogas slurry filter.The biogas slurry is filtered by the biogas slurry filter,and the filtered residue and filtrate are rationally utilized to solve the environmental pollution problem caused by improper treatment of the biogas slurry and the phosphating slag.The results show that the filter material has a good removal effect on the viscous organic matter in the biogas slurry.When the ratio of poplar wood chips to iron phosphate is 1:1,the filter material after calcination at 150 ? has the best filtration effect on the biogas slurry.At this time,the lower concentration of water-soluble total phosphorus in the lower layer filtrate can be used as liquid fertilizer..As the temperature increases and the amount of iron phosphate added increases,the filtration rate decreases,but the turbidity also decreases.