Preconcentration of gold by rice husk ash

The goal of this research was to develop a new, efficient adsorbent of gold-thiourea complex, [Au(CS(NH2)2]+. In this experiment, rice husk was heated at three different temperature: 300°C, 400°C and 500°C. Rice husk ash heated at 300°C adsorbed gold thiourea complex, whereas rice husk ash heated at 400°C and 500°C did not. The structure of rice husk ash heated at 300°C had specific silanol groups and oxygen functional groups of carbon, while rice husk ash heated at 400°C and 500°C contained siloxane groups. Maximum gold adsorption of rice husk ash heated at 300°C and activated carbon, was 21.12 and 33.27 mg Au/g adsorbent, respectively. However, rice husk ash absorbed 0.072 mg thiourea/g adsorbent, which was less than activated carbon adsorbed (0.377 mg thiourea/g adsorbent). In addition, the adsorbed gold could be eluted from this rice husk ash by sodiumthiosulfate more easily than from activated carbon. The results revealed that rice husk ash heated at 300°C can be used as a new adsorbent for gold thiourea complex.