flotation, lime, heavy metal extraction, PHMG, polyhexamethylene guanidine, precipitation


The method of metal ions' chemical precipitation using polyhexamethylene guanidine (PHMG) and calcium oxide (CaO) was employed for extracting metal ions from concentrated solutions. The order of reagent introduction was found to be crucial in the extraction process, with the best extraction efficiency observed when PHMG was added to water before CaO. This order of addition facilitated the polyelectrolyte effect, resulting in the unfolded conformation of macromolecules and enhancing their interaction with metal ions in solution. Optimal dosage ranges were determined, coinciding with the concentration interval of the polyelectrolyte effect, which maximized the flocculation ability and complex formation of PHMG. The combined use of PHMG and CaO, along with variations in pH, achieved high degrees of metal ion removal (>99%) in a single stage of solution treatment, except for chromium (Cr3+) and cobalt (Co2+). The surface activity of PHMG and ability to transfer metal ions as metal-polymer complexes supported its use in the flotation method for extracting heavy metal ions from low-concentration aqueous solutions. The kinetics of PHMG and metal ion removal by flotation showed rapid binding of metal ions to polymer macromolecules, and regression equations were established to describe the kinetics. The residual concentrations of metal ions after flotation met regulatory sanitary and environmental requirements for wastewater and drinking water.

A two-stage scheme for heavy metal ion extraction was developed, involving chemical precipitation and flotation extraction, with a pilot plant designed and manufactured for testing. During wastewater treatment in an electroplating production setting, metal ion concentrations that complied with regulatory standards were achieved.



Dias, F. G. G.; Pereira, L. F.; Parreira, R. L. T.; Veneziani, R. C. S.; Bianchi, T. C.; Fontes, V. F. N. P.; Galvani, M. C.; Cerce, D. D. P.; Martins, C. H. G.; Rinaldi-Neto, F.; Ferreira, N. H.; Silva, L. H. D.; Oliveira, L. T. S.; Esperandim, T. R.; Sousa, F. A.; Ambrósio, S. R.; Tavares, D. C. Evaluation of the antiseptic and wound healing potential of polyhexamethylene guanidine hydrochloride as well as its toxic effects. Eur. J. Pharm. Sci. 2021, 160, 105739. https://doi.org/10.1016/j.ejps.2021.105739

Liu, N.; Ren, P.; Saleem, A.; Feng, W.; Huo, J.; Ma, H.; Li, Sh.; Li, P.; Huang, W. Simultaneous Efficient Decontamination of Bacteria and Heavy Metals via Capacitive Deionization Using Polydopamine/Polyhexamethylene Guanidine Co-deposited Activated Carbon Electrodes. ACS Appl. Mater. Interfaces. 2021, 13 (51), 61669–61680. https://doi.org/10.1021/acsami.1c20145

Ojovan, M. I.; Lee, W. E.; Kalmykov, S. N. Treatment of Radioactive Wastes. In An Introduction to Nuclear Waste Immobilisation; Elsevier, 2019; pp 231–269. http://dx.doi.org/10.1016/B978-0-08-102702-8.00016-9

Park, J. H.; Choi, G. J.; Kim, S. H. Effects of pH and slow mixing conditions on heavy metal hydroxide precipitation. J. Korea. Org. Res. Recycl. Assos. 2014, 22, 50–56. https://doi.org/10.17137/Korrae.2014.22.2.50

Qasem, N. A. A.; Mohammed, R. H.; Lawal, D. U. Removal of heavy metal ions from wastewater: a comprehensive and critical review. npj Clean Water. 2021, 4, 36. https://doi.org/10.1038/s41545-021-00127-0

Yadav, M.; Gupta, R.; Sharma, R. K. Green and Sustainable Pathways for Wastewater Purification. In Advances in Water Purification Techniques; Elsevier, 2019; pp 355–383. http://dx.doi.org/10.1016/B978-0-12-814790-0.00014-4