Structure-adsorption relationships of phenyl- and benzylphosphonic acids and their esters on kaolinite:3D-QSAR study

Coal slime water treatment and resource recovery are vital for the sustainable development of coal industry sustainability. Kaolinite, over 60% of clay minerals in coal slime water, is key for high-value flotation utilization. Phosphonic-acid collectors adsorb effectively on kaolinite via -PO(OH)₂ groups, but their structural diversity (phenyl/benzylphosphonic acids and esters) blurs structure-adsorption relationships. Existing studies focus on single collectors for specific minerals, lack a systematic screening/prediction database, and rarely combine first-principle calculations with three-dimensional quantitative structure-activity relationship (3D-QSAR) to explore multi-type collector mechanisms on kaolinite. This study combined density functional theory (DFT) with 3D-QSAR to study phosphonic-acid collector adsorption on kaolinite (001). Comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) models were validated, with CoMSIA performing optimally (q² = 0.843, r² = 0.984). Diethyl (2-chlorobenzyl)phosphonate and (2-hydroxyphenyl)phosphonic acid in the test set showed prediction errors < 1%, confirming reliability. Two novel collectors (4-propylphenylphosphonic acid, 3-methyl-4-nitrophenylphosphonic acid) were designed, outperforming all database collectors, corroborating model validity and supporting high-efficiency collector development for kaolinite recovery.

First-principle calculations via Cambridge Serial Total Energy Package (CASTEP) yielded the adsorption energies of 35 phenyl/benzylphosphonic acids/esters on kaolinite (001) to build a molecular structure-adsorption database. The dataset was split into 80% training and 20% test sets post molecular energy minimization. CoMFA/CoMSIA models were built via partial least squares (PLS) regression, evaluated by q², r², F-statistic and standard error of estimate (SEE); contour maps analyzed molecular field effects. New collectors were designed via CoMSIA and DFT-verified.