Comparative Activation Process of Pb, Cd and Tl Using Chelating Agents from Contaminated Red Soils

Abstract

Adding chelating agents is a critical technique of heavy metal activation for enhancing phytoextraction through the formation of soluble metal complexes which will be more readily available for extraction. The preliminary, dynamic, equilibrium activation experiments and speciation analysis of Pb, Cd and Tl in contaminated red soils were used to select six chelates with relatively good activation performance from nine chelates, and the effects of dosage and pH on the heavy metals activation were studied systematically. Results showed that the activation of Pb, Cd and Tl by chelates reached equilibrium within 2 h, and the activation process showed three stages. Under neutral conditions, chelates had better activation performance on Pb- and Cd-contaminated soils. Except for S,S-ethylenediamine disuccinic acid (S,S-EDDS) and citric acid (CA), the maximum equilibrium activation effect (MEAE) of ethylenediaminetetraacetic acid (EDTA), N,N-bis (carboxymethyl) glutamic acid (GLDA), diethylenetriaminepentaacetic acid (DTPA) and aminotriacetic acid (NTA) was over 81%. The MEAE of Tl-contaminated soil was less than 15%. The decreasing order of the dosage of chelating agents corresponding to MEAE for three types of contaminated soils was Pb-, Cd- and Tl-contaminated soil, relating to the forms of heavy metals, the stability constants of metal–chelates and the activation of non-target elements Fe in red soil. Under acidic conditions, the activation efficiencies of chelates decreased to differing degrees in Pb- and Cd-contaminated soils, whereas the activation efficiencies of chelating agents in Tl-contaminated soils were slightly enhanced.

Phytoremediation of Cadmium: Physiological, Biochemical, and Molecular Mechanisms

“…In general, chelates are known as stimulating chelating agents in the release of divalent and trivalent cationic metals into soil water to enhance their absorption by the roots of plants. They are classified into three groups of (i) synthetic amino-polycarboxylic acids (APCAs), such as EDTA, ethylene-glycol-tetraacetic acid (EGTA) and sodium-dodecyl-sulfate (SDS); (ii) natural amino-polycarboxylic acids, including S,S-ethylene-diamine-disuccinic acid (EDDS) and nitrile-triacetic acid (NTA); and (iii) low molecular weight organic acids (LMWOAs) containing oxalic acid (OA), citric acid (CA), and tartaric acid (TA) [203][204][205].…”

Migration and Transformation of Heavy Metals in the Soil of the Water-Level Fluctuation Zone in the Three Gorges Reservoir under Simulated Nitrogen Deposition

“…e mechanism of N deposition-induced acidification of soil is different from acid deposition. Acidic deposition brings H + directly into the soil to activate trace metals, and the H + can displace the exchangeable fractions from their binding sites [26,27]. Different HMs have different sensitivity to acid deposition.…”

COMPARATIVE EXTRACTION OF Mn AND Pb USING EDTA AND CITRATE TO ASSESS THEIR MOBILITY FROM TWO DUMPSITES IN ZARIA METROPOLIS

“…The concentrations of extractable heavy metals and extraction yield varied considerably with the nature of complexing agent (Liu et al 2020). The removal efficiency was enhanced by the addition of a masking agent to stop the reaction of other ions such as Ca and Fe as their presence in the soil also interact with the complexing agent due to high concentrations and relatively high stability of their complexes.…”

“…The chemical substances which are of great environmental interest are the heavy metals. Heavy metals are of special interest because of the major risks they contribute to the environment, they enter human body through the food chain, causing serious hazards to lives (Liu et al, 2020). Heavy metals are toxic to humans as well as other organisms; they are released by metal-bearing soil constituents and migrate through the soil solution downward to the water table (Van Oort et al, 2006;Shina and Alok, 2010).…”