A sand composite with surface gel coating containing alkylamine toward the removal and immobilization of complex metal ions from electroplating wastewater

SiO 2 gel was formed on the grain surface of silica sand by hydrolysis and condensation of tetraethyl orthosilicate in water with the addition of 1-butylamine. The resultant product was a composite consisting of sand grains with mesoporous silica coating containing alkylamine inside. This composite exhibited basicity in the wastewater from copper electroplating due to its release of amine. As a result, the strongly acidic wastewater was neutralized and the co-precipitation of complex metal ions occurred. It was shown that up to 12 major metal ions in the wastewater could be simultaneously removed under static condition at room temperature by using the sand composite. The Fe and Cu in the wastewater could be removed completely, while the concentrations of Al, Cd, Ti, V, and Zn in the wastewater were reduced by two to three orders of magnitude. After the removal of multiple metal ions from the electroplating wastewater, the used sand was further applied as a raw material for making a silicate glass. The glass was chemically stable and thus the heavy metal ions from the wastewater were immobilized.