ハイドロタルサイト化合物を配合したコンクリートブロックによるリン除去

Abstract

Nutritive salts have to be removed from not only wastewater but also non-point water sources to inhibit the eutrophication of enclosed waters in the environment. However, efficient removal methods for nutritive salts from non-point sources have not yet been established. Here the authors reported that Mg-Al-Cl forms a hydrotalcite compound (HT) which has a high selectivity and a large adsorbing capacity for phosphate anions. Thus the authors developed some concrete materials mixed with HT for the removal of phosphorous from rivers, which is a main transport medium of nutritive salts in the non-point water sources. Four types of concrete blocks and mortar block, such as normal type, air-entraining type, large porous type and small porous type, were prepared by mixing cement with HT. The compressive strengths and phosphorous adsorption capacities of the blocks were investigated. The obtained results are as follows. 1) The compressive strengths of the concrete blocks and mortar blocks decreased with an increase in the amount of the HT mixed. However, the compressive strength of the porous-type concrete (HT-POC) and porous-type mortar (HT-POM) were almost equivalent to the strength value of 10 N·mm-2 by keeping the HT amounts below 100 and 160 kg·m-3, respectively. 2) HT-POC and HT-POM were found to have a large removal capacity and a rapid removal rate for phosphate anions with a wide range of concentrations at neutral pH. 3) Phosphate anions were removed through the anion exchange reaction of HT mixed in the concrete. 4) The amounts of phosphate anions removed by HT-POC and HT-POM were six and three times larger respectively than that of controls. 5) HT-POC and HT-POM adsorbed phosphate anion under the condition of coexisting CO32- and SO42-, which inhibited the phosphate anion exchange reaction of HT. These results suggest that HT-POC and HT-POM have a high feasibility as superior purification materials for the removal of phosphate anion from rivers.