|M.Sc Student||Yulia Gezik|
|Subject||Removal of Boron Compounds from Aqueous Solutions|
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Emeritus Narkis Nava|
Boron is an essential micronutrient for plants, but may be toxic when present in the soil solution. Relatively high boron concentrations in sewage effluents limit their reuse for irrigation. Conventional water treatment processes do not significantly remove boron from wastewater, where it originates mainly from the domestic use of washing powders and cleaning agents, and through the entrance of desalinated sea water into the water supplying network.
The main purpose of the research was to study physico-chemical treatment methods for the removal of boron compounds from aqueous solutions.
At first, the analytical methods of boron concentration determination were studied, and a spectrophotometric method, using Azomethine-H, was chosen. The method is fast, simple, reliable and its results are in a good agreement with the ICP method.
Boron adsorption on 4 mineral clays: kaolinite S-5, illite I-35, Ca-montmorillonite M-20 and Na-bentonite M-26; 3 types of aluminum oxide - activated alumina ALCOA F-1, neutral, acidic and basic, was studied in a batch system as a function of the time required to reach equilibrium, pH and concentration. Boron adsorption on calcium oxide, which reacts with water to form calcium hydroxide, was studied at high pH, and in the presence of concentrated acids.
For all the adsorbents boron removal was highly pH dependent, showing an optimal pH range for maximum adsorption, for mineral clays between pH 8-10, and for activated aluminas between pH 5-9, while equilibrium was reached after a few hours.
A good agreement to Langmuir adsorption isotherm was obtained in all the studies, and its constants were used to compare between different adsorbents. Calcium and aluminum oxides removed more boron than clay minerals, while the addition of concentrated sulfuric acid to calcium oxide and the activation process of alumina improved boron removal. Among the clay minerals, Ca-montmorillonite M-20 gave the best results, while kaolinite S-5 was the least effective. Basic activated alumina was the most successful adsorbent for boron removal.
Accordingly, activated alumina was chosen for the continuous adsorption experiment, including activation, adsorption and regeneration during a few cycles, and, similar to the batch experiment, basic activated alumina was proved to be the most efficient.
A short assay of boron in tap water around Israel shown concentrations below the guideline limit recommended by WHO, of 0.3mg B/L, with the exception of the city of Eilat, where high boron concentrations of 0.8 mg B/L were determined, which can also be damaging to the irrigated crops.