Sustainable Neutralization of Acidic Soapstock Wastewater Using Phosphorite Waste: Kinetic and Environmental Assessment

The acidic wastewater produced during cotton soapstock processing is a major environmental concern because of its low pH and high ionic strength. In this study, the feasibility of using Central Kyzylkum phosphorite waste as a sustainable mineral-based neutralizing agent was investigated under controlled batch conditions (333 K, 30 min). The experimental data revealed an increase in pH from 4.10 to 7.30, which corresponds to a neutralization efficiency of 78.05%, and an increase in CaO content from 23.92% to 36.96% (54.51% enrichment). Linear regression analysis (CaO = 3.4665·pH + 9.7852; R² = 0.911; F = 51.18; RMSE = 1.07%) revealed the strong statistical correlation between acidity stabilization and calcium activation. Residual analysis showed homoscedastic distribution and chemically controlled surface-mediated kinetics. Marginal analysis revealed the optimal operating ratio to be within the 100:25–100:35 ratio interval. The integrated Environmental Efficiency Index of 66.28% clearly shows that both acidity and mineral activation are achieved. The statistically validated and mechanistically consistent performance of the phosphorite waste clearly shows that it can be used as a sustainable alternative for the treatment of acidic industrial wastewater.