Flocculation of Cu, Mn, Ni, Pb, and Zn during estuarine mixing [Caspian Sea]

During estuarine mixing of fresh water with saline water and due to the flocculation process, a portion of dissolved metals come into particulate phase, and the dissolved load decreases. This process plays an important role in self-purification of heavy metals in rivers. In this study, flocculation of Cu, Mn, Ni, Pb and Zn during mixing of Cheshme-Kileh River water with Caspian Sea water has been investigated. Salinity and electrical conductivity are the governing factors for the flocculation of Mn and Cu. Zn and Ni are governed by pH. Dissolved oxygen is a governing factor for the flocculation of Pb. Rapid flocculation occurs in the earlier stages of mixing. The final flocculation rates of metals are in the following order: Mn [68.79%] > Pb [45.45%] > Ni [26.32%] > Cu [23.08%] > Zn [21.21%]. In addition, electro-flocculation [EF] is investigated. The results reveal that EF had adverse effect on flocculation rates of heavy metals. General pattern of EF of metals is like the following: Mn [57.89%] > Pb [40.9%] > Cu [23.08% > Ni [22.37%] > Zn [15.15%]. Furthermore, the effect of decreasing pH level on flocculation of heavy metals is studied. Except for Mn, decreasing the pH increased the flocculation rates of heavy metals. Maximum flocculation of Ni, Cu, Pb, and Zn occur at pH about 7.5. Due to the flocculation of trace metals during the estuarine mixing about 51.6, 7.8, 5.5, 3.9, and 3.6 ton/year of Mn, Ni, Zn, Pb, and Cu, respectively, are removed from the river water

Equilibrium sorption isotherm studies of Cd(II), Pb(II) and Zn(II) ions detoxification from waste water using unmodified and EDTA-modified maize husk

The mobilization of heavy metals in the environment due to industrial activities is of serious concern due to the toxicity of these metals in humans and other forms of life. The equilibrium adsorption isotherms of Cd(II), Pb(II) and Zn(II) ions, detoxification from waste water using unmodified and EDTA-modified maize husk have been studied. Maize husk was found to be an excellent adsorbent for the removal of these metal ions. The amount of these metal ions adsorbed increased as the initial concentration increased. Also, EDTA-modification enhanced the adsorption capacity of maize husk due to the chelating ability of ethylenediamine tetra acetic acid (EDTA). Among the three adsorption isotherms tested, Dubinin-Radushkevich isotherm gave the best fit with R² value ranging from 0.7646 to 0.9988 and an average value of 0.9321. This is followed by Freundlich and then Langmiur isotherms. The sorption process was found to be mostly a physiosorption process as seen from the apparent energy of adsorption which ranged from 1.03 KJ/mol to 12.91 KJ/mol. Therefore, this study demonstrates that maize husk which is an environmental pollutant could be used to adsorb heavy metals and achieve environmental cleanliness.