Direct Quantification of Sorption Thermodynamics of Phosphate on Four Soil Colloids through Isothermal Titration Calorimetry,ACS Earth and Space Chemistry

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Direct Quantification of Sorption Thermodynamics of Phosphate on Four Soil Colloids through Isothermal Titration Calorimetry
ACS Earth and Space Chemistry ( IF 2.9 ) Pub Date : 2021-01-21 , DOI: 10.1021/acsearthspacechem.0c00281
Zhineng Hong ₁ , Jing Yan ₁ , Jun Jiang ₁ , Jiuyu Li ₁ , Renkou Xu ₁

Affiliation

Sorption thermodynamics of phosphate (P) on the soil colloid remains poorly known, although many previous studies have been done by macroscopic, microscopic, and spectroscopic methods. Here, we directly determined effective thermodynamic parameters and explored the underlying mechanisms for P sorption on colloids extracted from four soils (two Oxisols, one Ultisol, and one Alfisol) at different pHs using isothermal titration calorimetry (ITC), together with batch sorption experiment, solution modeling, and surface characterization. The obtained results showed sorption thermodynamics and mechanisms highly dependent on pH and soil type. Sorptions of P on all the four soil systems over pH 5.0–8.5 were probably mediated by the ligand exchange that resulted in exothermic enthalpy (ΔH) values. By contrast, those at pH 3.5 were initiated by the ligand exchange with exothermic ΔH and a high equilibrium constant (k) followed by surface precipitation with endothermic ΔH and low k. The affinity of the examined soils to P, indicated by the k values, generally decreased with the pH level. Stronger affinity to P and greater availability of the surface site were observed for the Oxisols relative to Ultisol and Alfisol, which probably resulted from their differences in mineralogy and zeta potential. This study provides thermodynamic information for P sorption on soil colloids and indicates that ITC is useful for mechanistic investigations on ion sorptions.

中文翻译：

通过等温滴定量热法直接定量分析磷酸盐在四种土壤胶体上的吸附热力学

磷酸盐（P）在土壤胶体上的吸附热力学仍然鲜为人知，尽管以前的许多研究都是通过宏观，微观和光谱学方法进行的。在这里，我们直接确定了有效的热力学参数，并利用等温滴定量热法（ITC）探讨了从四种土壤（两种Oxisol，一种Ultisol和一种Alfisol）中提取的胶体上P吸附的潜在机理，并进行了分批吸附实验，解决方案建模和表面表征。所得结果表明吸附热力学和机理高度依赖于pH和土壤类型。pH在5.0〜8.5范围内的所有四种土壤系统对P的吸附都可能是由于配体交换而介导的，从而导致放热焓（ΔH）值。相比之下，pH 3.5的那些是由具有放热ΔH和高平衡常数（k）的配体交换引发的，然后是具有吸热ΔH和低k的表面沉淀。以k值表示的被测土壤对P的亲和力通常随pH值降低。相对于Ultisol和Alfisol，Oxisol对P具有更强的P亲和力和更强的表面位点，这可能是由于矿物学和Zeta电位的差异所致。这项研究为土壤胶体上磷的吸附提供了热力学信息，并表明ITC可用于离子吸附的机理研究。

更新日期：2021-02-18

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