Magnetic nano-hybrids adsorbents formulated from acidic leachates of clay minerals

Abstract Acid leaching of clay minerals provides a simple and industrially efficient route to produce active silica materials with different morphologies and functions on a large scale, but the generated acid leachate rich in metal ions has become a source of hazardous waste. Therefore, methods to treat or reuse it harmlessly become an emerging challenge. Here, a sustainable method to reuse the metal ions (i.e., Fe(II), Fe(III), Mg(II), and Al(III)) in the waste acid leachate of three representative clay minerals (palygorskite (Pal), montmorillonite (MMT) and nontronite (NNT)) for synthesizing 2D layered double hydroxide (LDH) was reported. The obtained Pal-LDH, MMT-LDH and NNT-LDH adsorbents can adsorb 127.16 ± 1.49 mg/g, 134.56 ± 3.49 mg/g and 123.20 ± 4.11 mg/g of Congo red (CR), respectively. The subsequent calcination treatment of LDH adsorbed CR produces three magnetic layered double oxides (LDO) with a 2D nano-layered shape and positive surface charges: Pal-LDO, MMT-LDO and NNT-LDO. The Pal-LDO adsorbent exhibits high adsorption capacities of 538.39 ± 4.23 mg/g for dye CR and 626.91 ± 4.89 mg/g for antibiotic tetracycline (TC). Using the adsorbent concentration of 0.50 g/L, the CR in the initial 100 mg/L dye solutions is removed completely. After adsorption, the adsorbent is easily recycled by exposing it to a magnetic field, regenerated by one-step calcination treatment and reused for the next adsorption cycle. After reuse 3 times, the resulting adsorbent still displays a good adsorption capacity of 350.67 ± 3.21 mg/g for the CR dye. Therefore, this study provides a new and universal approach to reuse the waste acid leachate of clay minerals and develop new recyclable adsorbents for the efficient decontamination of organic contaminants from wastewater.