Adsorption by and artificial release of zinc and lead from porous concrete for recycling of adsorbed zinc and lead and of porous concrete to reduce urban non-point heavy metal runoff

This report describes the use of porous concrete at the bottom of a sewage trap to prevent runoff of non-point heavy metals into receiving waters, and, secondarily, to reduce total runoff volume during heavy rains in urbanized areas while simultaneously increasing the recharge volume of heavy-metal-free water into underground aquifers. This idea has the advantage of preventing clogging, which is fundamentally very important when using pervious materials. During actual field experiments, two important parameters were identified: maximum adsorption weight of lead and zinc by the volume of porous concrete, and heavy metal recovery rate by artificial acidification after adsorption. To understand the effect of ambient heavy metal concentration, a simple mixing system was used to adjust the concentrations of lead and zinc solutions. The concrete blocks used had been prepared for a previous study by Harada & Komuro (2010). The results showed that maximum adsorption depended on the ambient concentration, expressed as the linear isothermal theory, and that recovery depended on the final pH value (0.5 or 0.0). The dependence on pH is very important for recycling the porous concrete. A pH of 0.5 is important for recycling both heavy metals, especially zinc, (8.0-22.1% of lead and 42-74% of zinc) and porous concrete because porous concrete has not been heavily damaged by acid. However, at a pH of 0.0, the heavy metals could be recovered: 30-60% of the lead and 75-125% of the zinc. At a higher pH, such as 2.0, no release of heavy metals occurred, indicating the safety to the environment of using porous concrete, because the lowest recorded pH of rainfall in Japan is. 4.0.