Heavy metal dissolution mechanisms from electrical industrial sludge

Viraj Gunarathne, Anushka Upamali Rajapaksha, Meththika Vithanage, Nadeesh Adassooriya, Asitha Cooray, Sudantha Liyanage, Bandunee Athapattu, Nishanta Rajakaruna, Avanthi Deshani Igalavithana, Deyi Hou, Daniel S. Alessi, Yong Sik Ok

Research output: Contribution to journalArticlepeer-review

14 Citations (Scopus)


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 sludge was investigated in the presence of three inorganic acids (nitric, sulfuric, and phosphoric) and three organic acids (acetic, malic, and citric) at concentrations ranging from 0.1 to 2.0 mol L−1. Sequential extraction indicated the presence of Cu primarily in the carbonate fraction, Pb in the residual fraction, and Ni in the Fe[sbnd]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 < sulfuric < acetic < phosphoric < citric < nitric. Acetic acid exhibited the highest release of Cu, at a rate of 72.62 × 10−11 mol m−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 the maximum rate of Ni release (0.23 × 10−11 mol m−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 the sludge. The results from our study emphasize that an understanding of the metal release mechanism is key to selecting the optimal acid for the maximum recovery of heavy metals.

Original languageEnglish
Article number133922
JournalScience of the Total Environment
Publication statusPublished - 2019 Dec 15


  • Industrial waste
  • Pollution mitigation
  • Resource recovery
  • Sludge treatment
  • Trace metals

ASJC Scopus subject areas

  • Environmental Engineering
  • Environmental Chemistry
  • Waste Management and Disposal
  • Pollution


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