Role of metal species in flocculation rate during estuarine mixing

Flocculation can be considered as an effective mechanism in self-purification of metals during estuarine mixing. In the present investigation, flocculation of metals during mixing of Minab River water with the Strait of Hormuz (The Persian Gulf) water is studied for the first time. Flocculation behavior of metals (except for Pb) is governed by dissolved organic carbon. The source of dissolved organic carbon is terrigenous in the estuarine waters of study area. The general pattern of flocculation of studied metals is manganese (180 mu g/L) > zinc (88 mu g/L)> nickle (73 mu g/L)> copper (30 mu g/L)> lead (19 mu g/L). The results of present study show that metal species are a very important factor in overall flocculation rate. It is found that solids and oxides have the highest and lowest flocculation levels, respectively. Eh-pH diagram indicated that lead is present as lead oxide in Minab River water and the least flocculation rate is attributed to this element. The results also showed that flocculation rate of metal species could be as solids > free ions approximate to hydroxides > oxides. The amount of metal flocculation is about 30.5, 6.6, 25.3, 10.4 and 62.5 ton/y for zinc, Pb, Ni, Cu and Mn, respectively.