Experimental Study On Solidification Of High-salt Wastewater With Cement Technology

As the terminal wastewater of power plants,desulfurization?FGD?wastewater has complex background,and the water quality and quantity characteristics are affected by many factors such as coal,limestone and desulfurization system operation,which is difficult to handle.The current mainstream zero-liquid discharge technology for desulfurization wastewater is divided into pretreatment,concentration reduction and transfer and solidification.The pretreatment mainly refers to the double alkali method,and the concentration reduction can be divided into two categories:membrane concentration and evaporation concentration.Transfer and solidification mainly includes evaporation crystallization,bypass evaporation and solidification/stabilization.The technology of solidification for desulfurization wastewater with cement meets the trend of zero-liquid discharge development,but only a small amount of research has focused on the solidification of heavy metal ions,even less research focused on the solidification of chloride ions.It is necessary to explore the factors affecting the solidification of high-salt wastewater with cement and the measures to improve the performance of blocks.According to the experiment mentioned above,a technical route for concentration by flue gas and solidification with cement of FGD wastewater is proposed.The single-factor experiment mixed simulated high-salt water with other materials to obtain blocks in order to explore the impact of the component materials on the properties of the blocks,The results show that the compressive strength reached the highest value when the cement ratio was 1.08,and increased when the fly ash ratio was greater than 0.25.The higher the ratio of high-salt brine,the lower the compressive strength.The rise range of cement to the Cl^-binding capacity of blocks was higher than the that of fly ash.Orthogonal experiment was carried out to investigate the influence of various factors on the properties of blocks,and the influence was ranked as follows:cement>high-salt brine>sand>fly ash.The experiment proved that the best mixing ratio is cement:fly ash:high-salt brine:sand=0.97:0.17:0.60:0.98.Experiments mixing with different water samples show that Cl^-increased the compressive strength of the blocks,and the sulfate in the concentrated FGD wastewater preferentially consumes some C₃A in cement,resulting in a significant decrease in the Cl^-binding capacity of blocks and an increase in the Cl^-leaching rate.Solidified blocks are suitable for non-reinforced material or curb instead of building materials with limited chlorine content because of the high content of free Cl^-in blocks.In the investigation experiment to improve the performance of the solidified blocks,Cl^-can greatly improve the compressive strength of the solidified blocks.When the concentration of Cl^-is 70,000 mg/L,the compressive strength of the solidified blocks is the largest,and the solidified blocks has the best performance;When the compound is blended,the improvement effect on the performance of the solidified blocks is not good,or even cause weakening condition;when the pH is 4,the compressive strength and the chloride ion leaching rate of the solidified body are the best.Therefore,it is necessary to adjust the pH to 4.0-5.0 with Ca?OH?₂ after the desulfurization wastewater is concentrated.Based on the experiments above,a technical route for concentration by flue gas and solidification with cement of FGD wastewater is proposed.The overall process was economically analysed in the premise of cement kerbstone being used as the final disposal,which proved that the technical route for concentration by flue gas and solidification with cement of FGD wastewater can bring environmental and economic benefits to the power plant at the same time.