Toxic metal adsorption from gold tailings wastewater using biowaste biochars: A circular economy approach

• The study assessed the adsorption efficiency of biowaste biochars for toxic metals from gold tailings wastewater. • The adsorption efficiency of corn cob biochar, peanut shell biochar for mercury in the gold tailings wastewater was greater than 90.0% at 20 min, 35 min and 50 min. • Biochar derived from corn cob biochar contains primary alcohol, alkane and carboxylic acids groups, peanut shell biochar contains aliphatic, tertiary alcohol, amine and secondary amines, and sheanut shell biochar (before adsorption) contains aliphatic, primary alcohol, amine and carboxylic acids groups. • Corn cob biochar, peanut shell biochar and sheanut shell biochar demonstrate considerable potential as adsorbents for effectively removing toxic metals from gold tailings wastewater, making a valuable contribution to the circular economy and the remediation of environmental pollution. Sustainable development of adsorbents from biowaste and their use for the treatment of wastewater is a circular economy approach. The study assessed the adsorption efficiency of biowaste biochars for heavy metal ions from gold tailings wastewater. Fourier transform infrared spectroscopy (FTIR) was employed to identify the functional groups and bond vibrations in the biowaste biochar. A total of 100 mL of the gold tailings wastewater was measured into a conical flask, and biowaste biochar dosage of 1.0, 2.0 and 3.0 g each was weighed and added, and then kept in a water bath at 30 °C and agitated at contact times of 20, 35 and 50 minutes. The corn cob biochar removes Cd (99.10 to 99.40%), Hg (90.50 to 93.80%), and Cr (15.60 to 75.60%) and Ni (21.30 to 84.50%), peanut shell biochar removes Cd (99.10 to 99.40%), Hg (90.60 to 93.80%), and Cr (19.10 to 77.80%) and Ni (35.50 to 85.30%) whilst sheanut shell biochar removes Cd (99.10 to 99.40%), Hg (89.40 to 93.80%), and Cr (8.90 to 73.30%) and Ni (35.50 to 87.10%). Corn cob biochar showed K F for Cd (3.4 × 10 11 to 1.8 × 10 17 mg/g), Hg (1.8 × 10 6 to 8.0 × 10 12 mg/g), and Cr (0.01 to 1.4 mg/g) and Ni (0.1 to 0.03 mg/g). The corn cob biochar contains primary alcohol, alkane and carboxylic acids groups, peanut shell biochar contains aliphatic, tertiary alcohol, amine and secondary amines, and sheanut shell biochar contains aliphatic, primary alcohol, amine and carboxylic acids groups. The biochar dosage increases the cadmium, mercury, chromium, and nickel adsorption efficiency onto biowaste biochars. The dosage, porous surface, and time increase the adsorption efficiency of cadmium, mercury, chromium, and nickel significantly. The Freundlich model was the best fit model for cadmium and mercury adsorption onto the biochars due to the heterogeneous surface of the adsorbent, which makes it have a tougher binding site. Biowaste biochars demonstrated considerable potential for effectively removing heavy metal ions from gold tailings wastewater, making a valuable contribution to the circular economy and the remediation of environmental pollution.