Green synthesis of reusable super-paramagnetic diatomite for aqueous nickel (II) removal

•The material (DECFASEs) was synthesized based on the concept of green chemistry.•The adsorbent has high adsorption capacity and Ni2+ can be rapidly removed.•Adsorbents showed stable adsorption capacity in repeated recycling tests.•Magnetic composites can be collected quickly and easily with external magnetic field.