Recycling of Waste Toner Powder as Adsorbent to Remove Aqueous Heavy Metals

The removal of Cd²⁺, Zn²⁺ and Ni²⁺ from metal solutions onto waste toner power (WTP) was investigated. The influence of parameters such as pH, contact time, initial metal concentration and adsorbent dosage was studied in batch adsorption experiments. Batch equilibrium experiments showed that the highest removal efficiency for Zn²⁺ and Cd²⁺ occurs at pH 7, while pH 5 is the most suitable for Ni²⁺ removal. The amount of metal removed (mg/g) improved when increasing the initial concentration, and sorption of heavy metals reached equilibrium in 24 h. Metals' uptake increased with increasing adsorbent dosage. The adsorption isotherms of Zn²⁺, Cd²⁺ and Ni²⁺ onto WTP fit the Langmuir better than the Freundlich model with correlation coefficient R² values ranging from 0.998 to 0.968 and 0.989 to 0.881, respectively. The data showed that the maximum adsorption capacity of heavy metals, a_max, ranged from 2.42 to 1.61 mg/g, from 6.22 to 2.01 mg/g and from 3.49 to 2.56 mg/g for Ni²⁺, Zn²⁺ and Cd²⁺, respectively, with the three WTPs used in this study. This adsorbent can potentially be used to remove metal ions from wastewater.