Transformation of Urea–Formaldehyde Resin Waste into Pb(II) and Cu(II) Adsorbent Toward a Circular Materials Economy Approach

Two potential hazardous substance problems are urgent to be solved. (1) Urea–formaldehyde resin waste that may produce various toxic compounds during conventional treatment; (2) Toxic heavy metal ions released in water that pose a severe threat to human health and ecosystems. Herein, innovative conversion of urea–formaldehyde resin waste into an effective adsorbent for hazardous heavy metal ions was achieved by a simple degradation–repolymerization method, toward a circular materials economy approach. The detailed effects of temperature and time on the degradation efficiency were studied. Plausible degradation mechanism was proposed. To increase the adsorption performance, the challenge of affording urea–formaldehyde resins with three-dimensional network structures was overcome by the ice templating. The effects of cooling rate and added water content on the morphology of urea–formaldehyde resin were investigated. Due to its three-dimensional network structure and high amine density, the prepared adsorbent exhibited removal rate up to 95.68% for Pb(II) and 80.80% for Cu(II), much higher than untreated urea–formaldehyde resin waste. The effect of solution pH on the adsorption performance of heavy metal ions was also discussed. Moreover, after five cycles, removal rates were still up to 81.34% for Pb(II) and 64.37% for Cu(II), indicating its good cycle stability. Its large source of raw materials, convenient conversion method, and high removal rate make this method extremely competitive in the areas of both polymer degradation and heavy metal ion removal.