Experimental study on preparation of autoclaved aerated concrete by replacing process water with desulphurization wastewater

The implementation of the "Water Pollution Prevention Action Plan 10" marks a higher demand for water environmental protection in China, and achieving a zero discharge of desulfurization wastewater has become a major trend in power plant environmental protection. Desulfurization wastewater has complex characteristics and is easily affected by operating conditions and coal types, making its treatment more difficult. Traditional evaporation and crystallization processes have high costs and serious problems with secondary pollution. Based on the analysis of desulfurization wastewater quality, this study proposes that the desulfurization wastewater is used to prepare autoclaved aerated concrete blocks, thus achieving the resource utilization of desulfurization wastewater and fixed salt. The prepared aerated concrete blocks can be sold as high-value building materials, bringing environmental benefits to power plants while creating economic benefits. The compressive strength and dry density of the aerated concrete blocks are used as evaluation indicators to explore the impact of factors such as desulfurization wastewater content, calcium-silicate ratio, cement-lime ratio, and desulfurized gypsum content on the performance of the concrete building materials. The results show that with the increase of desulfurization wastewater and desulfurized gypsum content, the product compressive strength decreases. The optimal calcium-silicate ratio and cement-lime ratio are 27∶70 and 16∶11, respectively. Through a four-factor three-level orthogonal test, the optimized water ratio is 0.75, and the optimal formula is fly ash: cement: lime: wastewater: midstream water = 73∶16∶11∶30∶45. The difference analysis shows that the influence order of each factor on solidified specific strength is: water ratio > wastewater content > calcium-silicate ratio > cement-lime ratio. Through the SEM, XRD, and FTIR analysis of hydrated products, it is found that the main products before steam compression are calcareous albite and Ca(OH)₂, and the products after steam compression are tobermorite, hydrogarnet, and calcium carbonate. The heavy metal leaching tests on block products show that all exceedances of heavy metals in five types of desulfurization wastewater meet the regulations. It is possible to prepare the autoclaved aerated concrete blocks with strength grade A5.0 and dry density grade B06 without harm to the environment from desulfurization wastewater, which provides a new path for the resource utilization of desulfurization wastewater.