Abstract
An enrichment procedure for trace amounts of gold in water utilizing the coagulation of soybean protein by adding acids or salts (calcium, magnesium, etc.) and its complex-forming character with heavy metal ions were investigated.
After adding fixed amounts of soybean milk (collector) and δ-gluconic lactone (coagulant) to a sample solution, the mixture was heated to boiling in order to coagulate the protein. The coagulum (soybean curd) was separated from the suspension with a centrifuge and burned to ashes with a low temperature plasma asher. Then the gold collected in it was determined by means of the atomic absorption and emission spectrographic methods. Effects of pH, the amounts of soybean milk added, and the concentration of NaCl in the sample solution on the recovery of gold were examined systematically. The best result was obtained under the following conditions : To a certain amount of sample containing more than 0.01 μg of gold, (2050) ml of 6.34% soybean milk was added and its pH was adjusted to 4.45.0 by adding the suitable amounts of δ-gluconic lactone. This pH range corresponded to the optimum pH for the coagulation of soybean protein. The recovery of gold was 99% or better. NaCl in the sample solution tended to decrease slightly the recovery of gold. The proposed method was applied to the determination of gold at the order of (0.011) ppb in the sample solutions such as water, 3% NaCl water and artificial sea water. This method was also applied to the determination of gold in common salts.
