Adsorption of arsenic by iron rich precipitates from two coal mine drainage sites on the West Coast of New Zealand

Abstract

Dissolved As can be strongly adsorbed to fine grained Fe(III) minerals such as hydroxides, oxyhydroxides and hydroxysulphates. Therefore precipitates that form during neutralisation or treatment of acid mine drainage have potential to be useful for treatment of As-contaminated water because acid mine drainage is often Fe rich. We tested the adsorption properties of Fe(III) rich precipitates from two West Coast coal mines with As-contaminated water from an historic gold ore processing site near Reefton. Precipitates were collected from distinctly different settings, an active acid mine drainage treatment plant at Stockton mine and the neutralisation/oxidation zone of acid mine drainage discharge at the abandoned Blackball Coal Mine. The two mine sites produce precipitates with different compositions and mineralogy. Arsenic adsorption onto precipitates from each site was determined in batch and column tests under laboratory conditions. Batch experiments indicate As adsorption occurs rapidly during the first 5 h and reaches equilibrium after 24 h. At equilibrium, and for a dosing ratio of 50 g of precipitate per litre of water, As concentrations decreased from 99 mg/L to 0.0080 mg/L with precipitates from Stockton and to 0.0017 mg/L with precipitates from Blackball. Arsenic adsorption capacity is up to 12 mg/g on precipitates from Stockton sludge and 74 mg/g on precipitates from Blackball. The Blackball precipitate adsorbs more As than precipitates from Stockton which is probably due to the higher Fe oxide content but pH and surface structure could also play a role. The column experiment confirmed that adsorption of As from a continuous waste stream onto these precipitates is possible, and that passive remediation using this waste product mixed with gravel to enhance permeability could be a viable approach at As-contaminated mine sites.

Arsenic (V) Removal by an Adsorbent Material Derived from Acid Mine Drainage Sludge

“…Fitting by the Langmuir model provides maximum As(V) adsorption capacities (q m ) for MIRESORB TM and GFH of 50.38 mg/g and 29.07 mg/g, respectively. The q m for the MIRESORB TM was higher than that reported in similar previous studies of AMDS, in which the As(V) adsorption capacity of AMDS was approximately 10-70 mg/g and varied with AMDS characteristics and experimental conditions [29][30][31]. A composite AMDS with organic binder material showed slightly decreased adsorption capacity.…”

Biological attenuation of arsenic and iron in a continuous flow bioreactor treating acid mine drainage (AMD)

“…The removal of arsenic concomitantly to Fe, so called "natural attenuation", has been 393 described in several AMD throughout the world (e.g. Cheng et al, 2009;Rait et al, 2010;394 Paikaray, 2015). In AMD, arsenic is generally removed from the dissolved phase by sorption 395 onto schwertmannite (Carlson et al, 2002;Fukushi et al, 2003;Ohnuki et al, 2004) or 396 formation of amorphous ferric arsenate (Maillot et al, 2013).…”

Start-Up and Performance of a Full Scale Passive System In-Cluding Biofilters for the Treatment of Fe, as and Mn in a Neutral Mine Drainage

“…The precipitates produced in laboratory bioreactors treating synthetic Lopérec mine water were composed of 2-line ferrihydrites with a few diffraction peaks indicating the presence of crystallized Fe(III) products, mainly hematite and goethite [22]. Ferrihydrite and goethite are both know to remove As by co-precipitation and adsorption in acidic waters [42] and by adsorption in neutral waters [43]. In contrast with Fe, As was immediately removed, certainly because the Fe/As ratio is more than enough to remove all As even if Fe precipitation was not complete.…”

“…Average dissolved As/Fe ratio in Lopérec water is 22.9 mg.g −1 . Rait et al [43] have shown that by adsorption only, Fe can remove arsenic up to 12 mg.g −1 in circumneutral water and up to 74 mg.g −1 in acidic water. Sekula et al [44] showed that ochreous precipitate from a circumneutral mine drainage contained up to 69 mg.g −1 As.…”