Electroflocculation of Metals during Estuarine Mixing (Caspian Sea)

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Abstract

ABSTRACT

Estuaries as a geochemical reactor can change the chemical forms of trace metals during the mixing of fresh and salt water. The flocculation process has an important role in self purification of heavy metals during estuarine mixing. In the present study, flocculation of metals (Cd, Co, Ni, Cr, and Pb) during mixing of Shefaroud River water with Caspian Sea water has been investigated. Except for Cr and Co, the flocculation of other studied metals in the Shefaroud River is controlled by redox potential, pH, and dissolved oxygen. Rapid flocculation occurs in the earlier stages of mixing (salinity of 0.4 to 1.2‰). The final flocculation rates of the studied metals are in the following order: Co (92.6%) > Ni (73.4%) > Cr 5 Pb (66.6%) > Cd (62.2%). In addition, electroflocculation (EF) is investigated under different voltage conditions. The results reveal that EF increases flocculation rates of Ni and Pb, and decreases removal of Cr and Co. The maximum reduction of studied metals is found in lower salinity (.1.2‰). Even though increasing voltage is expected to exhibit a positive effect on reduction of metals, increasing electrical potential puts the Co, Ni, and Cr removal into reverse. This study reveals that salinity and electrical conductivity have a reverse effect on removal of studied metals during flocculation and EF processes. The general patterns of flocculation of metals during EF processes are in the following order: at electrical potential of 6 V: Ni (95.5%) > Pb (94.4%) > Cd (62%) > Co (57.7%) > Cr (22.2%); at electrical potential of 12 V: Pb (94.4%) > Ni (92.8%) > Cd (64.4%) > Co (35.5%) > Cr (0%).

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