| Summary: | 碩士 === 國立成功大學 === 化學工程學系 === 103 === Boron is also used in several industrials, including the manufacture of borosilicate glass, detergents, semiconductor, fertilizers, and dyestuff production. However, the release of boron compounds into soil and ground water due to human activities generates many complex compounds with heavy metals. World Health Organization (WHO) defined an upper limit of 2.4 mg B/L for drinking water. Therefore, it is urgent to investigate the effective control of boron level in wastewaters before it is discharged into the environment.
The purpose of this study was to investigate and compare the performance between aluminum and nickel as electrode in electrocoagulation process for boron removal. The effect of different parameters, such as pH, electrode pairs, current density, initial boron concentration, supporting electrolyte type, and electrical energy consumption on the efficacy of electrocoagulation of boric acid were examined.
Results showed that the removal efficiency of boron increased from pH 4.0 to 8.0 and decreased at higher pH. The electrode with four pairs yielded the highest removal efficiency due to higher total surface area. Current density was the most important parameter affecting efficiency of boron removal, which increased with increasing current density from 1.25 to 5.0 mA/cm2, while the energy consumption also increased. Increasing solution concentration from 10 mg/L to 100 mg/L decreased the removal efficiency. NaCl as a supporting electrolyte performed better than Na2SO4 and NaHCO3 based on the efficacy of electrocoagulation. The mechanism of boron removal using electrocoagulation followed a second order kinetics. XRD analysis showed that the crystalline phase of precipitates was Al(OH)3 of bayerite and doyleite-types.
Meanwhile, Ni electrodes indicated a higher removal efficiency compared to Al ones. At the optimum condition (e.g. pH 8 and current density of 1.25 mA/cm2), boron removal efficiencies using Ni and Al electrodes were 94% and 72%, respectively. However, results showed that the concentration of dissolved nickel was higher than aluminum. On the basis of aluminum dose, electrocoagulation was proved as more reliable process compared to chemical coagulation for boron removal.
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