BayCEER Workshop 2015

Sustainable wastewater treatment: adsorption of toxic metals on granular schwertmannite

P 3.4 in Droughts, floods and hidden flowpaths: This research holds WATER

Introduction

The toxic oxyanions chromate and vanadate found in industrial wastewaters often require expensive and high-maintenance treatment. Passive filterbed systems that use the ferric oxyhydroxy sulfate schwertmannite as an adsorbent are a cheaper and very promising method. Schwertmannite can be sustainably produced from a waste product of mining and exhibits a high affinity to arsenate, an oxyanion that is structurally similar to chromate and vanadate. To make the application of the iron hydroxide in chromate and vanadate wastewater treatment possible, we determined the adsorption behaviour of both anions.

Material and Methods

Adsorption experiments were performed where 1 g/L granular schwertmannite was shaken for 8 days in solutions of pH 7 containing 890 µmol/L vanadate and 315 µmol/L chromate, respectively. Samples were taken from the solutions several times during the experiment. Reactions of schwertmannite in aqueous solutions were investigated in preliminary experiments.

Results

Both chromate and vanadate adsorbed on the granular adsorbent as well as on suspended, small-sized iron particles after 24 h. The latter were formed during the experiment due to schwertmannite transformation and, to a greater extent, because of mechanical abrasion of the iron hydroxide. Nevertheless, even after 5 days chromate and vanadate adsorption on granular schwertmannite exceeded that on particulate iron by 7 and 6 times, respectively. Consequently, mechanical abrasion did not significantly bias sorption properties. 39 % of the initial chromate and 73 % of the initial vanadate concentration was bound to the granular adsorbent after 5 days.

Conclusions

Schwertmannite was proven to be a good adsorbent for vanadate and a moderate one for chromate. However, prior to an application in industrial wastewater treatment research on the adsorption capacities of the oxyanions and of their sorption behaviour in column tests is required.

Keywords: Adsorption schwertmannite iron hydroxide Chromate vanadate industrial wastewater treatment