PURIFICATION OF FORMALDEHYDE FROM THE CIRCULATING WATER OF A METALLURGICAL ENTERPRISE: OVERVIEW OF METHODS AND TECHNOLOGIES

Abstract

This article provides a comprehensive overview of the problem of purification of recycled water from metallurgical enterprises from formaldehyde, a highly toxic pollutant typical for integrated industries. The main sources of formaldehyde entering the water cycle of the plant are analyzed in detail. It has been shown that in addition to classical pathways (destruction of binding resins in foundry production, presence of coke chemistry in above-ground waters), formaldehyde can be intentionally introduced into the process cycle as a reagent for decyanization of coke oven gas (Formex process) or removal of ammonia. It can also be unexpectedly formed as a by-product during incomplete oxidation complex organics by advanced oxidation methods. The main part of the paper systematizes modern methods of formaldehyde removal. Physicochemical approaches (bischofite reagent treatment), chemical approaches (classical Fenton reaction with generation of hydroxyl radicals), and innovative catalytic technologies are considered. Special attention is paid to promising developments, such as the use of silver–anion exchanger nanocomposites, which allow the oxidation of formaldehyde at room temperature with the possibility of multiple catalyst regeneration, as well as the use of metal nanoxides. Based on the analysis of scientific and patent information, it is concluded that it is necessary to use multi-stage purification schemes combining pre-coagulation with deep destructive methods. This not only reduces the formaldehyde content to the MPC level, but also to ensure the return of purified water to the production cycle. Therefore, the choice of the optimal technology for treating recycled water from formaldehyde should be based on a thorough analysis of the wastewater composition and a technical and economic comparison of various methods, with a focus on modern oxidative and catalytic technologies.