Prepared self-growth supported copper catalyst by recovering Cu (II) from wastewater using geopolymer microspheres

Abstract

Recycling metals from adsorbents is a promising strategy for utilizing metal resources with better efficiency, and improving environmental protection. In this work, NaOH-activated slag-based geopolymer microspheres (NaOH-SGS) were synthesized by the one-pot suspension solidification method. As regards Cu(II) adsorbents, their maximum adsorption capacity of 335.43 mg/g was much higher than other geopolymer materials. There are obvious changes after Cu2+ adsorption as follows. The average pore diameter of microspheres decreased from 19.91 to 10.80 nm; the pore volume increased from 0.05 to 0.27 cm3/g; the Brunauer−Emmett−Teller (BET) surface area increased from 8.23 to 91.72 m2/g; and the apparent morphology changed from gel-like layer to copper-containing nano-rods. As a result, the number of active sites for the adsorption of Cu2+ ions considerably increased. So self-growth adsorption process was named. Meanwhile the adsorbed Cu2+ species were evenly distributed on the NaOH-SGS surface. The spontaneous endothermic adsorption process which was mainly controlled by the diffusion through the external boundary layer was adequately described by the pseudo-second-order kinetic and Langmuir isotherm models. As to catalyst, the NaOH-SGS after Cu2+ adsorption (NaOH-SGS-Cu) was recycled and calcined (NaOH-SGS-Cu-calcined) to produce a supported copper catalyst that was successfully utilized to remove NO by CO. Although the optimum catalytic temperature for N2 selectivity (SN2 = 78.15%) and NO conversion (XNO = 91.96%) was a little high (350 °C), NaOH-SGS-Cu-calcined exhibits good sulfur resistance as slag contained a certain amount of sulfur. The obtained results indicated that the described method can be effectively used for copper recycling and the copper content of NaOH-SGS-Cu catalyst can be easily adjusted by varying the pH of solution, dosage, contact time, initial microsphere concentration and temperature. NaOH-SGS could be a bifunctional material (Cu2+ adsorbent and catalyst support).