沉积物离子交换法直接测定黄河口水体中溶解有机物的络合容量

DIRECT DETERMINATION OF COMPLEXING CAPACITY OF ORGANIC MATTERS DISSOLVED IN HUANGHE ESTUARY WATER BY THE HUANGHE ESTUARY SEDIMENT-ION EXCHANGE METHOD

本文提出用黄河口沉积物为固体交换剂直接测定黄河口水体中溶解有机物的络合容量的一种新方法,其特点为:(1)不必假设“有机配位体和金属有机络合物与固体粒子不发生交换(或吸附)”;(2)运用普遍的吸附(交换)等温式;(3)在pH7—8范围内,δ-MnO_2的交换率(E%)高达近100,不能测得正常形式的等温线,无典型意义,而采用黄河口沉积物则无此缺点。

A new method to determine the complexing capacity of water (sea water and river water) by ion/coordination particle exchange is proposed with successful application to Huanghe Estuary water.1. Calculation of complexing capacity: Suppose the complexation between organic ligand A and inorganic ligand L(L = CO32- , HCO3-, OH-, SO42-) and trace metal Mn+ (Cu2+,Zn2+ and Cd2+ etc.) take place in Huanghe Estuary water. By mass equalibrium, the overall Cu(II) concentrationwhere α is α coefficent, with the expression of by mass equalibr-ium again,If there are more than two organic ligands [A(1)],…, [A(p)] in the system, thenBy Eqs. (1) and (5), we haveWhen ignoring the kind of A, and i equal 1,the terms [MA] and [Mn+] can be calculated as follows:By the ion/coordination particle exchange isothermaM can be expressed as (i = 1,2):The plot of [Mn+]/[MA] vs [Mn+], it[Mn+] and [MA] are given, should be straight line with a slope of 1/[A]total and intercept of 1/βA[A]total (Figs. 4 and 6).Van den Berg calculated the term [Mn+] by means of Langmuir equation, whereas we calculated it by means of the universal isotherm equation (9) from the theory of stepwise ion/coordination particle exchange, because the experiment really shows a stepwise type isotherm(Figs. 1 and 5). Also this calculation seems successful in two types of experiment carried out in this work.2. In order to simplify the calculation, two designed experiments were carried out: (1) Huanghe Estuary sediment served as ion exchanger; (2) Low pH condition (for example, pH = 3.0) Should be kept during the experiment that the exchange amount of organic matter or organic metal complexes on solid particle was kept as low as possible and then could be ignored in this case.As a result, the complexing capacity is [A]total = 0.49μm(pH = 8.0) and the stability constants are logβA = 8.45 (pH = 8.0) and logβA = 3.62(pH = 3. l),both of them are in good agreement with the previous literature data.3. The complexing capacity and overall apparent stability constants of Zn(II) and Cd(II) are shown in table 1.Tab. 1 The complexing capacity and overall apparent stability constants for Mn+-HES(Huanghe Estuary water systems)The complexing capacity and apparent stability constants of Mn+-HES(Huanghe Estuary systems) are in the order:Cu(II) > Zn(II) > Cd(II) This result agrees with the work in the literature.