Differential determination of arsenic (III) and total arsenic with L-cysteine as prereductant using a flow injection non-dispersive atomic absorption device

Removal of hazardous ions from aqueous solutions: Current methods, with a focus on green ion flotation

Hazardous ions, like those of heavy metals, cause significant health and environmental problems when they are discharged into water resources naturally or through various industrial processes. Removing these ions from water is of significant importance in the provision of high-quality water for drinking and agricultural usage. This work discusses current techniques that are frequently used for the removal of heavy-metal ions from aqueous solutions by absorption, particularly the use of biodegradable surfactants in ion flotation. Certain new surfactants promise high efficiency in their use in the ion-flotation process and in their application in industrial-water treatment to remove heavy metals. As an example, this work demonstrates the high efficiency of surfactants based on an amino-acid (L-cysteine) in removing a range of heavy-metal ions in a simple, single-stage ion-flotation process. High foaming ability, the ability to operate in various temperatures and pHs, decomposing into natural products and high binding affinity for heavy-metal ions make the cysteine-based surfactants a highly suitable compound to replace current commercial surfactants in ion- and froth-flotation processes. Removal of particular ions can also be achieved in ion flotation; a suitable choice of parameters, such as pH and surfactant concentration, favours the surfactant binding to those ions. Further intensive work is required to develop an optimal process to recover valuable elements from waste solutions.

Low-Level Arsenic Removal from Drinking Water

The reported ability of cysteine and cystine to bind typical arsenic oxy-ions in water is used as a basis for a study of the potential for using a surfactant with a cysteine head-group for selective arsenic binding and removal in an ion flotation process. Several different head-group attachment methods are studied with cysteine and cystine and with single- and double-chain surfactants. A comparison of the properties of these surfactants with some other surface-active compounds, with groups like those on cysteine, suggest that few compounds have suitable characteristics for the efficient removal of low levels of arsenic from drinking water. An amino-acid-based single-chain surfactant is synthesized by reacting cysteine with octanoyl chloride to obtain octanoyl cysteine, which is then used in a study of selective ion flotation for the removal of low levels of arsenic from drinking water. This compound has high water solubility and causes extensive foaming in a typical flotation chamber and removed 99.4-99.9% of the 5 mg L-1 arsenic present in the contaminated water in a simple, single-stage ion flotation process, using either air or nitrogen gas. These laboratory results indicate that these surfactants can be useful in the large-scale treatment of low-level arsenic-contaminated water.