Chemical speciation and mobilization of copper and zinc in naturally contaminated mine soils with citric and tartaric acids

Abstract

A one-step extraction procedure and a leaching column experiment were performed to assess the effects of citric and tartaric acids on Cu and Zn mobilization in naturally contaminated mine soils to facilitate assisted phytoextraction. A speciation modeling of the soil solution and the metal fractionation of soils were performed to elucidate the chemical processes that affected metal desorption by organic acids. Different extracting solutions were prepared, all of which contained 0.01 M KNO(3) and different concentrations of organic acids: control without organic acids, 0.5 mM citric, 0.5 mM tartaric, 10 mM citric, 10 mM tartaric, and 5 mM citric +5 mM tartaric. The results of the extraction procedure showed that higher concentrations of organic acids increased metal desorption, and citric acid was more effective at facilitating metal desorption than tartaric acid. Metal desorption was mainly influenced by the decreasing pH and the dissolution of Fe and Mn oxides, not by the formation of soluble metal-organic complexes as was predicted by the speciation modeling. The results of the column study reported that low concentrations of organic acids did not significantly increase metal mobilization and that higher doses were also not able to mobilize Zn. However, 5-10 mM citric acid significantly promoted Cu mobilization (from 1 mg kg(-1) in the control to 42 mg kg(-1) with 10 mM citric acid) and reduced the exchangeable (from 21 to 3 mg kg(-1)) and the Fe and Mn oxides (from 443 to 277 mg kg(-1)) fractions. Citric acid could efficiently facilitate assisted phytoextraction techniques.

Effect of overlying water pH, dissolved oxygen and temperature on heavy metal release from river sediments under laboratory conditions

“…Previous studies found that the fraction of metal existing in exchangeable form have the highest mobility. Carbonate bound and Fe-Mn oxide bound metal fractions were sensitive to pH changes and more likely to mobilize and release from the sediment under low pH (Pérez--Esteban et al 2013, Equeenuddin et al 2013. Under the middle to alkaline pH in this research, most of the metals were partitioned into carbonate and Fe-Mn oxyhydroxides, thus the released metals in the overlying water should mostly come from exchangeable fraction.…”

“…Many researchers reported that at low pH the metal release was more obvious than at middle or high pH, however, the low pH instances are very rare in natural environment (Butler 2009, Watmough et al 2007, Pérez-Esteban et al 2013, Yang et al 2006, Jing et al 2007). So in this study, only middle and high pH effects were investigated.…”

Influence of Soil Chemistry and Plant Physiology in the Phytoremediation of Cu, Mn, and Zn

“…The authors concluded that the combination of two or more amendments was effective for improving phytoremediation of metal contaminated sites by Lolium perenne (Gunawardana et al, 2011). However, care should be taken when applying amendments to improve trace metal bioavailability because leaching to groundwater and thus groundwater pollution can occur (Perez-Esteban et al, 2013).…”

“…In general, organic acids can bind trace metal ions in soil solution by complexation reactions, making them more available for plant uptake (Wang and Zhong, 2011). However, organic acids can also reduce the soil pH and solubilize some non-labile fraction of trace metals in soil, thus enhancing trace metal availability (Perez-Esteban et al, 2013).…”

“…To improve the phytoremediation of Cu, Mn and Zn, the application of amendments (organics and inorganics) has been widely studied and has proven to be a useful way to manage some of the problems related to trace metal bioavailability and plant growth (Gunawardana et al, 2011;Najeeb et al, 2009;Perez-Esteban et al, 2013). Amendments can be used to enhance the bioavailability of trace metals, which will improve phytoextraction, or to reduce the labile fraction of trace metals, to assist in phytostabilization (Padmavathiamma and Li, 2010;Wu et al, 2012a).…”