| Phosphorus is an indispensable element in living organisms,but phosphorus resources are in danger of being in short supply.Due to their difficulty in recycling,according to statistics,phosphate ore is expected to be completed in the next 50 years.At present,many scholars have studied the recovery of phosphorus from surplus sludge from sewage treatment plants,biomass ash and volcanic ash.If the recovery of phosphorus resources can be achieved,the consumption of natural phosphate rock will be greatly relieved.Because of its own hazardous waste properties,fly ash has increased the difficulty of recovering phosphorus resources from it.While studying the recovery of phosphorus resources from waste incineration fly ash,it can transfer heavy metals from fly ash from solid phase to liquid phase.The disposal of fly ash is facilitated.This article first analyzed the physicochemical properties of fly ash from a municipal solid waste incineration power plant in Wuhan.Then,the wet chemical method was used to recover phosphorus resources from municipal solid waste incineration fly ash.Phosphorus in the fly ash was leached by acid-alkali combined leaching and hydrochloric acid leaching.Acid and alkali combined leaching was mainly considered in terms of pretreatment time and alkalinity.Concentration and leaching time;hydrochloric acid leaching mainly consider the solid-liquid ratio,leaching time and acid concentration on the phosphorus leaching efficiency.The main research object of phosphorus recovery is the leachate obtained under the optimum conditions of hydrochloric acid leaching,mainly adopting the secondary precipitation method to recover the phosphate ions in the leachate,adjust the pH to 3,perform a precipitation once to remove most of the interfering ions,and adjust the pH to 4Secondary precipitation crystallization was performed to recover phosphorus in the leachate.Finally,the adsorption characteristics of leaching residue in methylene blue simulated dye wastewater was studied,and the leaching of Pb and Cr in the supernatant was also discussed,which provided a theoretical basis for the further use of leaching residue.The results showed that the main components of waste incineration fly ash were SiO2（32.024%）,Al2O3（14.835%）,and CaO（16.72%）.The particle size was mostly between 125μm-250μm.The color was gray and dull,and the pH showed strong alkali.In toxic leaching experiments,ultrapure water was used as the leaching agent,and the leaching of Pb exceeded the standard value.When acetic acid solution was used as lixiviant,the leaching of Pb and Cd exceeded the standard value.The results also showed that the highest removal rate of calcium was only 12.6%under pretreatment.Under alkaline conditions,with the increase of pH,the leaching efficiency of phosphorus in pretreated fly ash increased,and the maximum leaching efficiency occurs at a leaching time of 3 h and an alkali concentration of 3mol/L.Under acidic conditions,as the pH increases,the leaching efficiency of phosphorus in the pretreated ash decreases.Taking into account the reaction time and cost,the optimal conditions obtained are hydrochloric acid concentration 2 mol/L,solid-liquid ratio 1:5,and leaching time 2 hours.The final phosphorous product of the secondary precipitation method contained 74%of the phosphorus content in the initial leaching solution.The phosphorus content of the product was 30.17 g/Kg,and the total recovery rate was 63.76%.Increased use of fly ash,leaching residue with large concentration of hydrochloric acid,and residue with large concentration of sodium hydroxide all increase the adsorption effect of methylene blue. |
