Preparation of a Solid Adsorbent Derived from Concrete Sludge and its Boron Removal Performance

Abstract

We prepared a solid adsorbent for boron removal using real concrete sludge. The sludge was diluted with water at dilution ratios from 1 to 15. The diluted concrete sludge was then filtered and dried. Two types of drying methods were examined: natural drying under atmospheric conditions and forced drying in an oven at 105 °C. The boron removal performance was examined using a boric acid solution containing 100 mgB/L. All of the adsorbents prepared showed boron removal capacity. The adsorbent prepared with dilution ratio 10 and forced drying exhibited the highest boron removal capacity; the boron concentration after 24 h was just 3.33 mg/L, which is below the Japanese standard for industrial effluent (10 mg/L), and the maximum adsorption capacity for boron was 50 mgboron/gadsorbent. The drying method had a significant effect on both the rate and capacity of boron removal. With natural drying under atmospheric conditions, the adsorption initially proceeded quickly, but the final amount adsorbed was lower than that for the force-dried adsorbents. The boron removal can be attributed to ion exchange and uptake of boron in the ettringite phase. These results indicate that boron adsorbents prepared from concrete sludge can be applied for the removal of boron from effluents.