Adsorption of Cd2+ Using Brick-Sludge Composite: A Circular Economy Approach

Cadmium (Cd), a highly toxic element, often contaminates drinking water through Cd²⁺ impurities in galvanized pipelines and cadmium-based solders. This study presents a sludge-brick composite for Cd²⁺ decontamination, aligning with circular economy principles. Using Response Surface Methodolo-gy (RSM), key parameters such as pH, mixing time, and sludge proportion (V/V) were optimized, with adsorption capacity (qe) as the response variable. The qe was evaluated by testing 0.1 g of the material in a 10-cc water sample at pH 7 over 1 hour. 50 g of sludge was dispersed in 250 cc of deionized water using ultrasound for 20 minutes. The prepared solution was then combined with an additional 250 cc of deionized water and stirred at 70°C for 2 hours at a speed of 300 rpm. Subsequently, sludge percent-age, the solution's pH and mixing time with 1 g of brick powder were adjusted based on the RSM pat-tern. The results of the RSM modeling indicated that a quadratic model with an R2 value of 0.8 and a predicted R2 of 0.7 provided a reliable framework for response optimization. ANOVA analysis re-vealed that sludge percentage had the greatest impact on adsorption efficiency, with an F-value of 5.17. pH was identified as the second most influential factor, followed by the mixing time of sludge and brick powder. The optimization analysis, achieving a desirability of 1, revealed that the highest Cd²⁺ adsorption performance onto the composite occurs under the following conditions: pH 7, a sludge-brick mixing time of 10 hours, and a sludge proportion of 48% during adsorbent synthesis