Removal of ionized nanosilver from wash water using emulsion liquid membrane process

Abstract

The increasing number of products containing nanosilver has raised a great concern over the public due to the release behaviour of ionized nanosilver which create the toxicity problems especially to the aquatic organism. Therefore, there is a necessity for the removal of ionized nanosilver from wastewater. One of the potential techniques is an emulsion liquid membrane process (ELM). This research investigated the extraction and recovery of ionized nanosilver from wash water using ELM process. The membrane phase contained kerosene as diluent, Cyanex 302 as a carrier, Span 80 as a surfactant and acidic thiourea as a stripping agent. The extraction was carried out in batch process using a mixer-settler and the recovery part was performed using a high voltage demulsifier. The ionization of nanosilver was determined using three variables which were effect of triethanolamine concentration, agitation speed and temperature. ELM stability was investigated at different surfactant concentration, ionic liquid concentration, agitation speed, homogenizer speed, emulsification time and extraction time. The parameter of extraction and recovery studied involving pH of external phase treat ratio, carrier concentration and stripping agent concentration. The optimization was done using response surface methodology (RSM) for the recovery process with three significant process variables. Results showed that almost 70% of nanosilver was ionized in the wash water. The most stable emulsion was observed at 3% w/v of Span 80, 150 rpm of agitation speed, 10,000 rpm of homogenizer speed and 5 minutes of emulsification and extraction time. Besides, almost 100% of ionized nanosilver was successfully extracted and the optimum conditions obtained for the recovery process using RSM were 0.256 treat ratio, 0.75 M sulphuric acid concentration and 0.85 M thiourea concentration. At this optimum condition, the maximum recovery of the ionized nanosilver was 84.74%. Thus, emulsion liquid membrane (ELM) method has a great potential in order to treat wash water containing ionized nanosilver.