Abstract:
In this paper, we investigate the release of heavy metals from sludge produced from an electrical industry using
both organic and inorganic acids. Single and sequential extractions were conducted to assess heavy metals in different
phases of the sludge. Metal release from sludgewas investigated in the presence of three inorganic acids (nitric,
sulfuric, and phosphoric) and three organic acids (acetic,malic, and citric) at concentrations ranging from0.1
to 2.0mol L−1. Sequential extraction indicated the presence of Cu primarily in the carbonate fraction, Pb in the residual
fraction, and Ni in the Fe\\Mn oxide fraction. The cumulative release rates of heavy metals (i.e., Pb, Cu, and
Ni) by 1.0 mol L−1 of acid increased with the use of the following acids in the order of: malic b sulfuric b acetic b
phosphoric b citric b nitric. Acetic acid exhibited the highest release of Cu, at a rate of 72.62 × 10−11 molm−2 s−1 at
pH 1, and malic acid drove the release of Pb at a maximum rate of 3.90 × 10−11 mol m−2 s−1. Meanwhile, nitric
acid provided themaximumrate of Ni release (0.23 × 10−11 molm−2 s−1) at pH 1. The high rate of metal release
by organic acids is explained through ligand-promoted mechanisms that enhance the release of metal ions from
