Study On Competitive Complexation Of Dissolved Organic Matter Between Metal Ions By Differential Spectroscopy

There are a large number of natural organic matter in various types of surface water and groundwater.In the process of water chemistry,on the one hand,natural organic matter controls the metabolism of microorganisms,generating water quality problems such as color and odor;on the other hand,natural organic matter is the main medium for pollutants to enter the water source.It provides a carrier for the transformation of inorganic pollutants like heavy metals,thereby improving the complexing ability and ion exchange capacity of soil and water.Studying the competitive complexation between natural organic matter and metal ions in the natural environment is the key to understanding the natural water chemical process,and is of great significance for studying the quality of drinking water and the water chemistry in natural environment.In this study,UV-visible differential spectroscopy and NICA-Donnan model were used to quantitatively study the complexation of different metal ions with NOM.The contribution of different metal ions to NOM complexation was calculated by using PIKAIA software.In this paper,we researched in the effects of the competitive complexation of several metals(like Fe³⁺and Al³⁺,hardness cations and Eu²⁺,hardness cations and Fe³⁺,hardness cations Ca²⁺and Mg²⁺)with SRHA under different conditions like pH,background ion concentration,competitive ion concentration,ionic strength,and adding order,and the complexing ability of natural organic compounds with different metal ions was explored.The main results are as follows:?1?Quantitative characterization of the complexation of metal ions with natural organic matter in natural water is achieved by UV-visible differential spectroscopy and the established spectral parameters?lnA₄₀₀ and?Slope_350-400 by NICA-Donnon model.The PIKAIA software can characterize the contribution of the complexation of different metal ions with natural organic matter.On this basis,the competitive complexation of metal ions with natural organic matter is revealed.?2?Under the weak acidity?pH=6?and neutral conditions,Fe³⁺strongly inhibits the combination of Al³⁺and SRHA,while under acidic conditions?pH=5?,Al³⁺can react more with NOM,reducing the combination of Fe³⁺with SRHA.The adding order of coagulant addition also affects the complexation of Fe³⁺with NOM;under acidic?pH=5?and neutral conditions,hardness cations can combine with SRHA much better,preventing Eu²⁺from participating in the complexation with SRHA,especially Mg²⁺.Under the neutral condition,hardness cations can hinder the complexation of Fe³⁺with SRHA,Mg²⁺in particular,and the competitiveness is strengthened with the increase of hardness cation concentration;in alkaline environment?pH=9?,Mg²⁺can complex better with SRHA than Ca²⁺.At the same time,as the ionic strength increases,the complexation of hardness cations with SRHA is reduced.?3?This paper provides ideas for the study of complexation of natural organic matter and hydrochemical processes in the natural environment,and proposes a new method for drinking water treatment.