Experimental Study on the Direct Removal of Cadmium from Aqueous Solution Using Peanut-Activated Biochar without Residual Rinse

Abstract

The use of agricultural waste to produce low-cost activated carbon (AC) adsorbents for cadmium ion (Cd²⁺) removal in sewage has drawn more attentions. Conventionally, for biochar activated by alkaloids, pH adjustment is required, and it involves operations, such as washing and sieving. Given that wastewater containing Cd2+ is typically acidic, the adsorption experiment of Cd2+ must be conducted immediately after the preparation of AC, which may lead to crucial improvements in the current treatment process for Cd2+-containing sewage. To explore the direct application process of biochar prepared through alkaloid-impregnated activation for the removal of Cd²⁺ in water, this study used peanut shells as a raw material (RM) and potassium hydroxide (KOH) as a modifier/activator to prepare biochar. After subjecting the peanut shells to activation with low-concentration KOH and pyrolysis at 600 °C, proximate analysis and surface morphology comparison of the obtained biochar were performed. Meanwhile, the untreated biochar and 10% KOH-AC were used in adsorption experiments, with a scanning electron microscope utilized for the surface study. The results show the following: (1) Sieving can effectively eliminate ash from AC but has limited improvement on the removal rate of Cd²⁺ (Cd-RR) and cause mass loss, which reduces the comprehensive removal efficiency. (2) The 10% KOH-activated biochar at 3.0 and 1.0 g/L achieves the best Cd-RR of 99.15% and 98.99%, respectively. The crushed KOH-impregnated peanut shell AC can remediate Cd²⁺ wastewater directly and has advantages in terms of RM cost, preparation process, and removal benefits compared with traditional ones. The conclusions provide a novel method for the treatment of Cd²⁺- containing sewage using peanut shell AC.