Prepared self-growing supported nickel catalyst by recovering Ni (Ⅱ) from metal wastewater using geopolymer...

Here, new and effective microsphere adsorbents were synthesized by NaOH activating slag based geopolymer (Na-SGS). These microsphere adsorbents upset the adsorption equilibrium with the maximum Ni²⁺ adsorption capacity of 414.38 mg/g which is much larger than that of other geopolymer materials. After Ni²⁺ adsorption from simulated nickel electroplating wastewater, more active positions for the adsorption Ni²⁺ ions on Na-SGS were provided as shifts from the average pore diameter of 22.00-7.44 nm, the pore volume of 0.06 to 0.25 cm³/g, the Brunauer-Emmett-Teller (BET) surface area of 10.46-125.35 m²/g and the apparent change of new morphology. Moreover, the adsorbed Ni²⁺ species were distributed uniformly on Na-SGS. Thermodynamic performance reflected an exothermic, spontaneous and molecular disorder adsorption process, which can be easily controlled by the pH, dosage, initial concentration, contact time and temperature. Through the controllable adsorption, Na-SGS after Ni²⁺ adsorption (Na-SGS-Ni) was recycled and then reduced to be directly supported nickel catalysts (red-Na-SGS-Ni), which showed superior catalytic activity for CO₂ methanation. Although the highest percent of CO₂ conversation (XCO₂ =99.54%) and methane selectivity (SCH₄ =99.5%) are both at 300 °C, red-Na-SGS-Ni performed good XCO₂ (99.48%) and SCH₄ (98.2%) at low temperatures (100 °C).