Experimental design strategy to model the adsorption of toxic metals from industrial wastewater onto untreated Giri-clay-based adsorbent via response surface methodology

This study aimed to gain a deeper understanding of the adsorptive properties of Giri natural clay, thereby expanding knowledge of novel adsorbents and facilitating the design of an optimal adsorption system. This study employed response surface methodology (RSM) to model and assess the adsorption of Cr⁶⁺ and Pb²⁺ from industrial wastewater using Giri‑clay, a low‑cost adsorbent. The Giri-clay-adsorbent was characterised comprehensively using Fourier transform infrared spectroscopy, Energy dispersive X-ray spectrometry, Scanning electron microscope and X-ray diffraction. The influence of four process variables: adsorbent dosage (A), initial metal concentration (B), solution pH (C), and contact time (D), was examined through a central composite design (CCD). Optimization of process variables identified that the highest Pb²⁺ removal of 83.76 % occurred at A = 32.50 mg, B = 62.50 mg L⁻¹, C = 8.00, and D = 45.00 min, while the maximum Cr⁶⁺ removal of 71.51 % was achieved at A = 77.50 mg, B = 87.50 mg L⁻¹, C = 8.00, and D = 45.00 min. A comparison between model predictions and experimental data yielded high correlation coefficients (R² = 0.9455 for Cr⁶⁺ and 0.7814 for Pb²⁺), demonstrating that the developed models reliably predict toxic‑metal removal by Giri‑clay