Effects of organic acids on heavy metal release or immobilization in contaminated soil

In order to explicit the environmental activity of heavy metals affected by different organic acids in soil,a batch incubation experiment was explored to investigate the influence of high relative molecular mass organic acid(HMWOA)(humic acid and fulvic acid)and low relative molecular mass organic acid(LMWOA)(threonic acid and oxalic acid)on the release or immobilization of Pb,Cu and Cd in soils.Results showed that LMWOA,especially threonic acid,had a good performance in the release of Pb,Cu and Cd from soils,and decrease in the fractions of HOAc-extractable,reducible and oxidable Pb,Cu and Cd.Conversely,HMWOA,especially humic acid,decreased the release of Pb,Cu and Cd,while it increased the fractions of HOAc-extractable,reducible and oxidable Pb,Cu and Cd,indicating that HMWOA can immobilize heavy metals.The release of Pb,Cu and Cd caused by LMWOA was attributed to the dissociation of soil organic matter and amorphous iron oxides since the total organic carbon and the water-soluble iron increased.The immobilization of Pb,Cu and Cd by HMWOA was attributed to the adsorption onto HMWOA followed by amorphous iron since HMWOA resulted in a significant decrease of zeta potential and an increase of amorphous iron oxide.It can be concluded that LMWOA has a potential application in soil washing remediation,while HMWOA can be used in the immobilization remediation for heavy metals contaminated soils.

Preparation of Fe-As alloys by mechanical alloying and vacuum hot-pressed sintering:microstructure evolution,mechanical properties,and mechanisms

Arsenic materials have attracted great attention due to their unique properties.However,research concerning iron-arsenic(Fe-As) alloys is very scarce due to the volatility of As at low temperature and the high melting point of Fe.Herein,a new Fe-As alloy was obtained by mechanical alloying(MA) followed by vacuum hot-pressed sintering(VHPS).Moreover,a systematic study was carried out on the microstructural evolution,phase composition,leaching toxicity of As,and physical and mechanical properties of Fe-As alloys with varying weight fractions of As(20%,25%,30%,35%,45%,55%,65%,and 75%).The results showed that pre-alloyed metallic powders(PAMPs) have a fine grain size and specific supersaturated solid solution after MA,which could effectively improve the mechanical properties of Fe-As alloys by VHPS.A high density(> 7.350 g·cm^(-3)),low toxicity,and excellent mechanical properties could be obtained for FeAs alloys sintered via VHPS by adding an appropriate amount of As,which is more valuable than commercial Fe-As products.The Fe-25% As alloy with low toxicity and a relatively high density(7.635 g·cm^(-3)) provides an ultra-high compressive strength(1989.19 MPa),while the Fe-65% As alloy owns the maximum Vickers hardness(HVo.5 899.41).After leaching by the toxicity characteristic leaching procedure(TCLP),these alloys could still maintain good mechanical performance,and the strengthening mechanisms of Fe-As alloys before and after leaching were clarified.Changes in the grain size,micro structure,and phase distribution induced significant differences in the compressive strength and hardness.