Dynamic desorption of arsenic from polymer-supported hydrated iron(III) oxide in a wastewater treatment plant.

Polymer-supported hydrated iron(III) oxide (PHIO) was successfully applied as adsorbent for arsenic removal in a wastewater treatment plant in Nandan, China. The practical PHIO adsorbent samples (PHIO-P) were collected from the adsorption column of the wastewater treatment plant, and desorption experiments of the adsorbent were carried out. Our results showed that the formation of precipitates on the surface of PHIO-P might block the porous channel of the adsorbent and decrease its arsenic adsorption capacity. In the dynamic arsenic desorption experiment, the arsenic desorption equilibrium was achieved more quickly at decreasing desorption velocity, and higher arsenic desorption efficiency was obtained at increasing NaOH concentration in regenerant. It was found that the PHIO-P adsorbent could be well regenerated at 1.0 M NaOH solution and desorption velocity of 5 BV h-1. Comparing with the raw adsorbent, the maximum arsenic adsorption capacity of PHIO-P decreased by 41.1% after practical running for 26 months. Additionally, the frequently used waste PHIO adsorbent could be treated as non-hazardous material in the arsenic-containing wastewater treatment process after long-time use.

Adsorption characteristic of As(III) on goethite waste generated from hydrometallurgy of zinc.

In this paper, goethite waste from hydrometallurgy of zinc was used as a raw material for arsenic adsorbent preparation. The goethite waste adsorbent (GWA) was characterized with scanning electron microscope (SEM), X-ray powder diffraction (XRD), and particle size distribution analysis. The adsorption of As(III) on GWA was studied as a function of contact time, pH, and coexisting anions. The safety of GWA usage in the wastewater treatment process was assessed by toxicity characteristic leaching procedure (TCLP) tests. The equilibrium adsorption data fitted well with the Langmuir isotherm model, and the maximum adsorption capacity of As(III) on GWA was 51.47 mg.g-1. GWA showed higher adsorption capacity at weak alkaline pH values (7.0-9.5). The coexisting PO43- and SiO32- presented significant adsorption competition with As(III) in aquatic systems. No significant heavy metals leaching was observed for GWA and As(III) loaded GWA in TCLP tests, which implied the safety of GWA as an adsorbent for arsenic containing wastewater treatment.

Cadmium adsorption characteristic of alkali modified sewage sludge.

This paper proposed a new biosorbent preparation method by alkali modification of sewage sludge. The cadmium ion (Cd(2+)) adsorption capacity of alkali modified sewage sludge (AMSS) was evaluated by equilibrium sorption experiments. The amount of released calcium ion (Ca(2+)) in sorption equilibrium experiment were measured in order to reveal the adsorption mechanism. In addition, Zeta potential, specific surface area and Fourier transform infrared (FTIR) spectra of AMSS were tested. The results showed that the cadmium adsorption isotherms of AMSS fitted well with both Langmuir and Freundlich models, and the maximum adsorption capacities increased by 0.713 mmol g(-1). The cadmium adsorption capacity of biosorbent increased with NaOH solution concentration (range from 0.25 to 7.5 mol L(-1)) for sewage sludge modification. The strong cadmium adsorption of AMSS was attributed to ion exchange effect, electrostatic attraction and complexation. This alkali modified sewage sludge may have a potential for serving as cadmium removal biosorbent.