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

Study of the suspending process with the use of a conical mixer through the example of the process of sulfuric acid neutralization at Sviatogor JSC

Summary

The process of suspending solid particles in a liquid by means of mechanical mixing is considered. A technique for the selection of mixing devices with account of the geometry of the mixer has been developed and described. The methodology is based on the semi-empirical Zwietering model, supplemented in the course of additional studies by Ayranchi and Kresta. Various modes of the suspending process have been studied. On the basis of theoretical relationships, a conical mixer with a special blade geometry was developed and tested in laboratory conditions resulting in a highly efficient suspending process. The empirical suspending coefficient of Zwietering and Ayranchi–Kresta was calculated resulting in the possibility to calculate the required parameters of the mixer on a scale of industrial reactors. The efficiency of the new mixing device was proved during industrial tests in a chemical reactor for quenching sulfuric acid with lime milk. Owing to the use of a conical mixer the reaction rate was reduced from 60 to 38 minutes with a 40% reduction in electricity consumption. It is proved that a sufficient condition for the enhancement of the neutralization process will be eliminating the sedimentation of the suspended sludge to the bottom of the reactor, i.e. the suspending process in the bottom part shall be enhanced.

Key words

sulfuric acid , conical mixer , mixing , suspending , neutralization

Results of studying the removal of heavy metal ions from industrial wastewater

Summary

The results of studies on the removal of heavy metal ions from acid-base wastewater of electroplating industry by neutralization, sedimentation and filtration are presented. During a laboratory experiment carried out with processing real acid-base wastewater of one of the enterprises in Samara with caustic soda, the optimal pH range found was 9.8–10.6. Using a flow through model of a vertical settling tank, the calculated hydraulic size of the suspension generated during the alkalization of the given wastewater category was determined that can be taken as 0.28 mm/s. The level of heavy metal ion removal in the process of galvanic wastewater treatment according to the flow scheme «pH adjustment – settling tank – filter with granular media» was experimentally determined in mg/l as: total iron 0.42–0.97; copper 0.028–0.087; nickel 0.016–0.073; zinc 0.047–0.28; cadmium 0.006–0.016. At the same time, the requirements for receiving industrial effluents into the Samara municipal sewer were met only for iron; whereas, the concentrations of other metals ranged from 0.85 to 13.3 shares of the permissible concentrations; therefore, in order to achieve the established standards, additional treatment was required, for example, by sorption.

Key words

wastewater , hydraulic size , filtration , galvanic production , heavy metal ions , neutralization