Species dependent aqueous biphasic extraction of some heavy metals

Evolution of Environmentally Friendly Strategies for Metal Extraction

The demand for the recovery of valuable metals and the need to understand the impact of heavy metals in the environment on human and aquatic life has led to the development of new methods for the extraction, recovery, and analysis of metal ions. With special emphasis on environmentally friendly approaches, efforts have been made to consider strategies that minimize the use of organic solvents, apply micromethodology, limit waste, reduce costs, are safe, and utilize benign or reusable materials. This review discusses recent developments in liquid- and solid-phase extraction techniques. Liquid-based methods include advances in the application of aqueous two- and three-phase systems, liquid membranes, and cloud point extraction. Recent progress in exploiting new sorbent materials for solid-phase extraction (SPE), solid-phase microextraction (SPME), and bulk extractions will also be discussed.

Extraction and separation of tungsten (VI) from aqueous media with Triton X-100-ammonium sulfate-water aqueous two-phase system without any extractant

An aqueous two-phase system composed of Triton X-100-(NH₄)₂SO₄-H₂O was proposed for extraction and separation of tungsten(VI) from aqueous solution without using any extractant. The effects of aqueous pH, concentration of ammonium sulfate, Triton X-100 and tungsten, extracting temperature on the extraction of tungsten were investigated. The extraction of tungsten has remarkable relationship with aqueous pH and are to above 90% at pH=1.0-3.0 under studied pH range (pH=1.0-7.0) and increases gradually with increasing Triton X-100 concentration, but decreases slightly with increasing ammonium sulfate concentration. The extraction percentage of tungsten is hardly relevant to temperature but its distribution coefficient linearly increases with increasing temperature within 303.15-343.15K. The distribution coefficient of tungsten increases with the increase of initial tungsten concentration (0.1-3%) and temperature (303.15 K-333.15K). The solubilization capacity of tungsten in Triton X-100 micellar phase is independent of temperature. FT-IR analysis reveals that there is no evident interaction between polytungstate anion and ether oxygen unit in Triton X-100, and DLS analysis indicates that zeta potential of Triton X-100 micellar phase have a little change from positive to negative after extracting tungsten. Based on the above-mentioned results, it can be deduced that polytungstate anions are solubilized in hydrophilic outer shell of Triton X-100 micelles by electrostatic attraction depending on its relatively high hydrophobic nature. The stripping of tungsten is mainly influenced by temperature and can be easily achieved to 95% in single stage stripping. The tungsten (VI) is separated out from solution containing Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Al(III), Cr(III) and Mn(II) under the suitable conditions.

A novel smart microsphere with magnetic core and ion-recognizable shell for Pb2+ adsorption and separation

Smart core-shell microspheres for selective Pb(2+) adsorption and separation have been developed. Each microsphere is composed of a Pb(2+) recognizable poly(N-isopropylacrylamide-co-benzo-18-crown-6-acrylamide) (PNB) shell and a magnetic Fe3O4 core. The magnetic PNB core-shell microspheres show excellent Pb(2+) adsorption selectivity among the coexisting Cd(2+), Co(2+), Cr(3+), Cu(2+), Ni(2+), Zn(2+), K(+), and Ca(2+) ions by forming stable B18C6Am/Pb(2+) host-guest complexes and exhibit an interesting temperature-dependent Pb(2+) adsorption. The inner independent magnetic Fe3O4 cores enable the Pb(2+)-adsorbed microspheres with a magnetically guided aggregation to be separated from the treated solution using a remotely controlled manner. The isothermal Pb(2+) adsorption result fits well with the Freundlich isotherm. The magnetic PNB core-shell microspheres show very fast adsorption of Pb(2+), and the adsorption process of Pb(2+) onto magnetic PNB core-shell microspheres fits well with the pseudo-second-order model. Moreover, Pb(2+)-adsorbed microspheres can be regenerated by simply increasing the operation temperature and washing with deionized water. The proposed magnetic PNB core-shell microspheres provide a promising candidate for Pb(2+) adsorbents with selectively separable and efficiently reusable abilities.