Activation of the mineralized mass of Central Kyzylkum using acidic wastewater from the oil and fat industry: Freundlich-based adsorption kinetics for fluorine release

Abstract

This study investigates the simultaneous utilization of mineralized mass (MM) from Central Kyzylkum phosphorite waste and acidic wastewater (AWW) from the soapstock processing industry for efficient fluoride removal. The MM was chemically activated by AWW under controlled conditions, leading to surface modification, increased porosity, and enhanced active site heterogeneity. The chemical interaction between H⁺ ions from AWW and fluorapatite in MM resulted in ion exchange, dissolution of phosphate groups, and the formation of volatile HF. Adsorption experiments were conducted at various MM: AWW ratios to determine the optimal operating parameters. Equilibrium data were fitted to the Freundlich isotherm model, confirming multilayer adsorption on heterogeneous surfaces. Kinetic analysis indicated that the pseudo-second-order (PSO) model provided the best fit, suggesting that chemisorption is the dominant rate-limiting mechanism. The Weber–Morris intra-particle diffusion model revealed that pore diffusion contributes to fluoride uptake but is not the sole controlling step. The synergy between isotherm and kinetic results supports a two-stage adsorption process involving rapid surface chemisorption followed by slower intraparticle diffusion. The developed method offers a dual environmental benefit by valorizing two industrial waste streams and reducing their ecological footprint. The produced sorbent showed high fluoride removal efficiency under simulated operational conditions. The process is simple, cost-effective, and compatible with existing industrial infrastructures. Large-scale application has the potential to reduce operational costs and promote circular economy principles. These findings provide a sustainable approach to water treatment in fluoride-affected regions while addressing industrial waste management challenges.