The introduction provides the general description of the ecological and economic feasibility of silicon carbide (SiC) regenerating from silicon-containing waste and purification of washing solutions of the regeneration process of heavy metal ions is substantiated. The research’s purpose and tasks are formed, the scientific novelty and the practical significance of the obtained results have been determined.
The first part focuses on the hazardous effects of toxic heavy metals (Fe (III), Cu(II), Zn(II), Pb(II), Cd(II)), conducted an analysis of existing methods of water purification of heavy metal ions with a summary of different ways comparison. A critical analysis of separation and deposition methods of suspensions using flocculants is presented with the advantages in latest researches.
The origin of various silicon-containing wastes, their processing and utilization are analyzed. The technological requirements for the chemical and granulometric composition of silicon carbide for further use are given. The method of leaching heavy metals from silicon-containing waste with chloride acid is proposed and the efficiency of using polyhexamethyleneguanidine (PGMG) as a flocculant for the reagent-flocculation method of washing solutions cleaning from leaching is substantiated.
Thus, a comprehensive approach is proposed for the SiC regeneration from silicon-containing cuttings, which involves:
- technical requirements attainments for the chemical and granulometric composition of regenerated SiC required for the further use of SiC in metallurgical industries;
- purification of the obtained rinsing solutions of the SiC regeneration process from heavy metal ions by the reagent-flocculation method using calcium hydroxide and the flocculation properties of PGMG for sedimentation and filtration of metal hydroxides-pollutants.
The second part presents the experimental methods, the experimental and laboratory plants description, used materials, equipment, and chemical reagents for washing solutions cleaning of leaching of the silicon carbide regeneration process.
The third part presents studies results characterize the interaction of metal ion-pollutants with PGMG.
A method of polarography was used in which the recovery of Cu(II), Zn(II), Pb(II), Cd(II) ions from solutions with and without PGMG was investigated.
It has been established that Pb(II)-PGMG and Cd(II)-PGMG polarization causes only the corresponding aqua complexes limiting current of recovery reduction, there is no shift in the half-wave potential of the recovery process. Reducing the value of the limiting recovery current can indicate the Cd(II) and Pb(II) with PGMG interaction to form difficult soluble compounds that do not take part in the recovery process.
It was found that the zinc polarographic restoration from the Zn(II)-PGMG system and the compartment with the Cu(II)-PGMG systems occur with a significant negative shift in the half-wave potential (-660 mV) for Z (II)-PGMG and (-181 mV) for Cu(II)-PGMG) compared with cathode reduction of Zn(ІІ) and Cu(ІІ) from aqua complexes. In addition, a sharp decrease in the compounds of type Zn(II)-PGMG and Cu(II)-PGMG diffusion current with an increase in the PGMG concentration, most likely, indicates the low soluble compounds transition into the precipitate.
The soluble complex compounds of the type [MeOH-PGMG]+ for Cu(II) and Zn(II) formation and the interaction of Pb(II) and Cd(II) with PGMG with the formation of [MeOH-PGMG]C1 slurry soluble hydroxosаlts was found.
Investigation by pH measurement method of changing the pH of the medium of a mixture of solutions of metal-pollutants (Cu(II), Zn(II), Pb(II), Cd(II)) with a solution of PGMG showed a decrease in the pH of the reacting system, which confirms the metal ions interaction with guanidine group of PGMG by replacing the hydrogen ion (H+) with the hydrolyzed metal ion (Me(OH)+). The chemical bond formation between Fe(III) and PGMG was investigated by spectrophotometry.
Conclusions on the interaction of metal ion-pollutants, obtained by polarography methods, pH measurement, spectrophotometry, are substantiated by IR-spectrometric studies of Me-PGMG-aggregates. The complex compounds formation of Fe(III), Cu(II) and Zn(II) from PGMG and compounds of Pb(II), Cd(II) with PGMG as hydroxyls has been confirmed.
To find out the feasibility of using PGMG as a flocculant, the study of the dose of PGMG influence on the rate of sedimentation of metal hydroxides of pollutants was carried out, and the concentration optimum of PGMG ((5,2 ÷ 7,8) mg/dm3) was established for the deposition proc
