Using Sawdust as a Sustainable Adsorbent for Removing Toxic Heavy Metals from Aqueous Solution

Background: The Environmental Protection Agency (EPA) sets the maximum allowable dose for thallium in drinking water at 0.002 mg/L, and notes that chronic exposure leads to hair loss, kidney damage, and liver and heart disorders, depending on the severity and duration of exposure. This paper aimed to remove thallium ions from aqueous solutions using sawdust as a low-cost adsorbent. Methods: White poplar wood sawdust was prepared and used as an adsorbent. The experiments were conducted in batch adsorption unit at different pH levels, contact times, agitation speeds, temperatures, initial concentrations, and doses of sawdust. Results: The maximum thallium removal efficiency was 92.12% conducted at pH 6, contact time 150 min, agitation speed 450 rpm, thallium initial concentration 90 ppm, temperature 25 °C, and sawdust dosage 6 g. Morphological tests showed that thallium ions exploited almost all active sites of sawdust, and the surface area decreased by about 95% after adsorption. FT-IR and SEM tests confirmed that sawdust contains various functional groups such as -OH and -COOH responsible for the adsorption. The isothermal and kinetic results exhibited a better agreement with Langmuir and intra-particle diffusion models, respectively. Thermodynamically, the adsorption was of negative ΔS and ΔG values at all temperatures, while ΔH was −176 kJ/mol. Conclusion: The study demonstrated that raw wood shavings can be used as an effective adsorbent to remove toxic thallium ions from contaminated aqueous solutions.