Ash and slag wastes of coals as promising sorbents of metal ions

Summary

The toughening requirements to the efficiency of wastewater treatment containing heavy metal ions call for searching new physical and chemical methods using inexpensive available materials as sorbents. The results of using ash and slag wastes generated at the heat and power plants operated by PJSC Irkutskenergo in Bratsk during the combustion of brown coal of the Irbeisk deposit in the process of removing iron (III) and aluminum ions from simulated solutions by sorption purification are presented. The specified wastes are not dangerous and have the form of a heterogeneous mixture of various mineral formations, predominantly calcium and magnesium carbonates (more than 50% by weight). Separate simulated solutions containing Fe³⁺ and Al³⁺ ions were prepared from state standard reference samples. The pH value was measured by the potentiometric method using Anion 4100 ion meter with silver chloride and glass electrodes. Iron and aluminum were determined according to the accepted methods. The results of the laboratory experiments have shown that the process of removing metals is accompanied by neutralization and alkalization of initially acidic solutions. The pH values obtained in this case exceed the initial values of metal hydroxide precipitation approaching pH of their complete precipitation with the addition of optimal amounts of ash and slag wastes. It is shown that the precipitated metal hydroxides are poorly soluble; therefore, if stored at the site of the sludge dump, they will have no negative impact on the environment. It has been established that the purification efficiency, depending on the process parameters, is 93–99 and 80–95% for Fe³⁺ and Al³⁺, respectively.

Key words

sorption , neutralization , ash and slag waste , Irbeisk brown coal , simulated water , residual concentration of iron (III) and aluminium ions