Proton Binding and Cadmium Complexation Constants for a Soil Humic Acid Using a Quasi‐particle Model
Proton Binding and Cadmium Complexation Constants for a Soil Humic Acid Using a Quasi‐particle Model
复制标题
DOI：
10.2136/sssaj1996.03615995006000040015x
复制
发表时间：
1996-07
影响因子：
2.9
通讯作者：
K. Bolton;S. Sjöberg;L. Evans
中科院分区：
文献类型：
--
作者：
K. Bolton;S. Sjöberg;L. Evans
为了更好地了解镉（Cd）在土壤中的命运，确定土壤腐殖质对镉在土壤中滞留的影响是很重要的。在这项研究中，利用电位滴定法研究了从土壤中提取的腐殖酸组分的酸碱性质和镉络合特性。考虑了多种静电和非静电平衡模型，以获得能最好地描述滴定数据的最简单模型。所有质子结合常数和镉络合常数均使用计算机程序FITEQL中的优化程序确定。与实验数据最吻合的模型是非静电模型，它包括两种二元酸，H₂A和H₂B。H₂A的解离常数计算为logβ₋₁,₀,₁,₀ = - 4.00 ± 0.02和logβ₋₂,₀,₁,₀ = - 9.32 ± 0.03，H₂B的解离常数计算为logβ₋₁,₀,₀,₁ = - 7.43 ± 0.24和logβ₋₂,₀,₀,₁ = -16.66 ± 0.31。该模型表明存在四种镉络合物，CdHA⁺、CdA⁰、CdH⁻¹A⁻和CdHB⁺，其络合常数计算为logβ₋₁,₁,₁,₀ = - 1.29 ± 0.09、logβ₋₂,₁,₁,₀ = -5.92 ± 0.07、logβ₋₃,₁,₁,₀ = -14.39 ± 0.09和logβ₋₁,₁,₀,₁ = - 3.72 ± 0.18。
In order to better understand the fate of Cd in soils it is important to ascertain the influence of soil humic substances on the retention of Cd in soils. In this study the acid-base and Cd complexation properties of a humic acid fraction extracted from a soil were investigated using potentiometric titrations. A number of electrostatic and nonelectrostatic equilibrium models were considered in order to obtain the simplest model that would best describe the titration data. All proton binding and Cd complexation constants were determined using the optimization procedure in the computer program FITEQL. The model that best fit the experimental data was a nonelectrostatic model, which included two diprotic acids, H2A and H 2 B. The dissociation constants for H 2 A were calculated to be log β -1,0,1,0 = - 4.00 ± 0.02 and log β -2,0,1,0 = - 9.32 ± 0.03 and for H 2 B were calculated to be log β -1,0,0,1 = - 7.43 ± 0.24 and log β -2,0,0,1 = -16.66 ± 0.31. The model indicated the presence of four Cd complexes, CdHA + , CdA°, CdH -1 A- and CdHB + , with complexation constants calculated to be log β -1,1,1,0 = - 1.29 ± 0.09, log β -2,1,1,0 = -5.92 ± 0.07, log β -3,1,1,0 = -14.39 ± 0.09, and log β -1,1,0,1 = - 3.72 ± 0.18.