高岭石等粘土矿物对五氯苯酚的吸附及其与矿物表面化合态关系

Adsorptions of pentachlorophenol onto clay minerals and relationship with their surface speciation

高岭石、蒙脱石和伊利石三种粘土矿物对五氯苯酚的吸附实验研究表明,其pH等温线为峰型曲线,三种矿物在pH<3时基本不吸附,在pH≈5或6时有一吸附峰,此后在pH≈6.5或7时有一低值,当pH>7时,高岭石和蒙脱石两矿物吸附量又表现出上升趋势。三种矿物表面位的化合态分析证明,吸附属于表面络合型,其峰型特征起因于矿物表面两种羟基位的化合态浓度和五氯苯酚的离子态浓度均随溶液pH变化而变化。

Pentachlorophenol(PCP)is widely used as an antiseptic and germicide in wood processing,medicin e and other industry area.The PCP belo ngs to the hydrophobic ionizable org anic compounds(HIOCs ),and its consumption in the world is largest a mong the phenol compounds and its toxicity is most drastic.The HIOCs offe r a unique opportunity to study the importance of chemical structure on the s orption mechanism,especially for t he sorption in soil or minerals.In this paper the sorption of pentachlorophenol onto kaolinite,montmorilloni te and illite is investigated and the results show that their pH-depending adsorption isotherms are not one of the adsorption-edge but a special peak-type with the range of 3～8of pH in solution.The peak positions are at pH≈5for kaolinite and montmorillonite,but at pH≈6for illite,and the adsorption peak-values are 0.24,0.12and 0.03mmol /kg,respectively.Based on the acid-basic titration data of these minerals a nd the PCP dissociation constant p K a (4.75)the speciation distributions of the surface siliane>SiOH and aluminane>AlOH on the surfaces of kaolinite,montmorillonite and illite,as well as the pentachlorophenol in solutio n are drawn out in relation to pH.Those figures clearly illustrate that the peak-type isotherms are resulted fr om the variations of the both speciations of two surface hydroxyls as well as of penta chlorophenol when the pH changes in s olution during sorption.Based on all experimental data,including the co ncentrations(in mol /L)of PCP speciation in solution,and th e surface speciation concentration(in mol /g)of the surface hydroxyls as well as th e sorption values(in mol /g)of PCP onto these minerals,a multi-component f itting calculation is made with corr elation coefficients better than 0.710for three types of surface complexes>AlOH -L,>SiOH -L and>SiO -HL(L and HL are dictated as ionized speciation and molecular speciatio n of PCP),that may be encountered during sorp tion,and their complexation reaction constants are 6.7,2.5×10 2 and 1.5×10 2 L /mol for kaolinite,8.5×10,2.5×10 2 and 7.9×10 2 L /mol for montmorillonite,and 3.1×10,2.8×10 2 and 6.2×10 2 L /mol forillite,respectively,whi ch indicate that the PCP may prefer to adsorb onto the sili ane site of those minerals to form the surface complex.