Effects of Corn Straw on Heavy Metals Release and Bioavailability in Coal Gangue
In order to study the effect of straw on the release and bioavailability of heavy metals in coal gangue,different proportions(0%,1%,2%,5%,10%)of corn straw were added to coal gangue to study their effects on the release and forms of heavy metals such as iron(Fe),manganese(Mn),copper(Cu),zinc(Zn),lead(Pb),and cadmium(Cd)in coal gangue.The results showed that the addition of corn straw promoted the rapid release of Fe and Mn in coal gangue,and the higher the proportion of straw addition,the higher the concentration of Fe and Mn in the leachate.At the end of the experiment(180 days of straw decomposition),the concentration of Fe and Mn in the treatment group with 10%straw addition reached 459.30 mg/L and 47.30 mg/L,respectively.The addition of corn straw overall promoted the release of Cu and Zn in coal gangue,inhibited the dissolution of Pb in coal gangue,but had no significant effect on the dissolution of Cd.Overall,the addition of straw promoted the transformation of Fe and Mn from reducible to exchangeable and oxidizable states in coal gangue,and the transformation of Cu from exchangeable and reducible states to oxidizable state,resulting in the transformation of Zn from reducible to exchangeable states.The heavy metal RAC risk assessment results showed that the proportion of active forms in each heavy metal was in the order of Mn>Zn>Cu>Fe>Cd>Pb.The addition of straw increased the proportion of Mn and Zn activity in coal gangue,and the treatment group with a straw addition of 5%had the lowest proportion of Cu and Cd activity in coal gangue.In summary,the addition of 5%corn straw has a fixing effect on Cu,Pb,and Cd in coal gangue,but it also activates Mn and Zn in coal gangue.When using corn straw for remediation and improvement of coal gangue,attention should be paid to the changes in Mn and Zn activity in coal gangue to prevent secondary pollution to the environment.
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