Study on phosphorus recovery and struvite synthesis from municipal sludge pyrolysis residue

An experimental study on the recovery of phosphorus resource was carried out for the resource application of sludge residue. The effects of acid species and different leaching conditions on the leaching of phosphorus from sludge residue were systematically analyzed，and the effects of pH and n（Mg）∶n（N）∶n（P） on the synthesis of struvite from the solution containing phosphorus were investigated. The results showed that the leaching rate of phosphorus from sludge residue could reach 96.9% under the conditions of liquid/solid ratio of 20 mL/g，hydrochloric acid concentration of 0.4 mol/L and leaching time of 4 h. Moreover，the crystallization rate of the phosphorus purification solution purified by cation exchange resin could reach 98.1% at pH=10，n（Mg）∶n（N）∶n（P）=1.2∶1.2∶1，and the heavy metal content in the obtained struvite met the standard limit of Organic and Inorganic Compound Fertilizer （GB/T 18877-2020）. In summary，79% of phosphorus in sludge residue could be recovered after phosphorus extraction，purification and crystallization.