An improvement of Cr⁺⁶ removal by the reduction to Cr⁺³ in Birjand ground water treatment

Abstract

Birjand is a city in the east of Iran. Underground water is the only drinking water source, because this city is in a dry region.Ground water hexavalent chromium ion (Cr +6 ) concentration in Birjand is about 0.07 mg/l, which is higher than the maximum contamination level (MCL). The maximum contamination level of Cr +6 is 0.05 mg/l according to WHO guidelines.In an effort to comply with the World Health Organization (WHO) guideline regulations governing hexavalent chromium, Cr +6 was reduced to Cr 3 through standard jar test procedures with the addition of ferrous sulphate as a reducing agent. This research studied this as a bench scale.In the first alternative, ferrous sulphate was just used as a reducing agent. A chromium concentration of 0.042 mg/l was reached in order to comply with WHO guidelines. But the addition of ferrous sulphate induced a sulphate ion (SO 4 2-) concentration increment of up to 430 mg/l, which is higher than the maximum contamination level according WHO guidelines (400 mg/l).In the second alternative, ferrous sulphate was used as a reducing agent with lime milk.A chromium concentration of 0.015 mg/l was reached with a sulphate ion concentration of 380 mg/l, which is less than the MCL (400 mg/l).

Microdetection of Chromium Mixed–Valences using CuNi/Ti Electrode and Linear Sweep Voltammetry

“…Voltammograms of the mixed-valence electrolyte of Cr 3+ and Cr 6+ for 1 and 10 μgL -1 are shown in Figure 12b. The Cr 6+ has a more negative potential than Cr 3+ due to its standard potential 45 and is more mobile in an aqueous solution 46 . The ions with a more negative reduction potential tend to be deposited on the electrode surface with a more positive reduction potential.…”