Time filter

Source Type

Christchurch, New Zealand

Weisener C.G.,University of Windsor | Weber P.A.,Solid Energy New Zealand Ltd.
New Zealand Journal of Geology and Geophysics | Year: 2010

Environmental contamination from mines producing acid rock drainage, which is caused by sulphide mineral oxidation, represents one of the most significant environmental problems facing the international mining industry. This work investigates the mineral morphological effects on the rate of pyrite oxidation and the influence of relict morphological features on rapid oxidation and thus acid generation rates. Laboratory-based kinetic tests were performed on potentially-acid forming rock by measuring changes in pyrite mineralogical compositions, metal release and acid generation over time. The rate of pyrite oxidation is strongly dependent on the reactivity of two pyrite morphological forms (euhedral and framboidal). After 210 days 70-100% of all framboidal pyrite had undergone complete oxidation, which contributed to an initial high acid generation rate (peak concentration of 2927mg L-1 CaCO3 after 120 days); subsequent acid generation rates (1730 mgL-1 CaCO3 after 390 days) were substantially lower. Scanning Electron Microscopy (SEM) micrographs clearly show the persistence of larger euhedral pyrite grains as a contributing factor to this on-going acidity after 390 days. Samples collected from laboratory humidity cells after 390, 480 and 720 days showed evidence of preferential dissolution associated with these large pyritic overgrowth textures. Clearly evident are prior relict framboid networks within larger euhedral pyrite grains suggesting that oxidative dissolution may be related to internal crystallographic defects associated with the overgrowth textures in these samples. © 2010 The Royal Society of New Zealand.

Gray D.,University of Canterbury | Harding J.,University of Canterbury | Lindsay P.,Solid Energy New Zealand Ltd.
New Zealand Journal of Marine and Freshwater Research | Year: 2016

Rivers receiving acid mine drainage (AMD) are frequently depauperate in fish and impacts may extend long distances downstream. AMD inputs may form chemical barriers for migratory species and isolate fish in unimpacted headwaters. We investigated the response of a diadromous fish, kōaro (Galaxias brevipinnis), to remediation of an AMD tributary in a 5th order river in New Zealand. A 2005 survey indicated limited recruitment of kōaro in the river likely due to the chemical barrier of AMD. By 2010, water treatment in the contaminated tributary had raised pH from a median value of 4.3 to 6 and reduced metals in the lower river, notably aluminium from a median of 2.48 to 0.41 mg/L. In 2012, kōaro density had increased by an order of magnitude relative to 2005. Furthermore, a greater proportion of juvenile fish were present. These results indicate that large-scale remediation of discharges can reverse the impacts of AMD on fish migration. © 2016 The Royal Society of New Zealand

Olds W.E.,University of Canterbury | Olds W.E.,Solid Energy New Zealand Ltd. | Tsang D.C.W.,University of Canterbury | Tsang D.C.W.,Hong Kong Polytechnic University | Weber P.,Solid Energy New Zealand Ltd.
Water, Air, and Soil Pollution | Year: 2013

Acid mine drainage (AMD) generated by some coal mines in New Zealand is currently treated by the addition of alkaline reagents which neutralize acidity, triggering the precipitation of dissolved metals as insoluble hydroxides. Some trace metals (Ni, Zn, Cu, Cd, and Pb) are discharged into receiving water bodies due to incomplete hydroxide precipitation at circum-neutral pH. This study investigated the incorporation of lignite-derived humic substances (HS) for metal complexation and removal during AMD treatment by Ca(OH)2 and CaCO3 neutralization. For Ca(OH)2 neutralization, addition of HS (regardless of dosing sequence) enhanced the removal of Zn, Cu, and Cd, probably due to the incorporation of metal-humate complex into settling flocs (via aggregation, co-precipitation, and adsorption) that were subsequently removed by sedimentation. However, additional removal of Ni and Pb was statistically indeterminate, which was ascribed to the low complexation affinity of Ni and high removal of Pb by adsorption onto Fe/Al hydroxides. Conversely, for CaCO3 neutralization, addition of HS only marginally enhanced Cd removal, with the removal of metals probably dominated by adsorption onto the abundant undissolved calcite. Equilibrium speciation modelling showed that about 25% and 38% of the remaining Cu and Pb in the treated AMD were complexed with HS, while only 5% of remaining Cd and less than 1 wt% of remaining Ni and Zn were organically complexed. In the AMD-receiving water bodies, about 20 mg l-1 of HS would be required for complete complexation (>95%) of Cu and Pb and 50 mg l-1 for Cd, whereas Zn and Ni complexation would not occur at natural stream HS concentrations. © 2013 Springer Science+Business Media Dordrecht.

Tsang D.C.W.,University of Canterbury | Tsang D.C.W.,Hong Kong Polytechnic University | Olds W.E.,University of Canterbury | Olds W.E.,Solid Energy New Zealand Ltd. | Weber P.,Solid Energy New Zealand Ltd.
Journal of Soils and Sediments | Year: 2013

Purpose: The aim of this study was to enhance the soil remediation of timber treatment sites; the potential application of biodegradable chelating agents and humic substances as enhancing agents was assessed in terms of the residual leachability of chromium, copper and arsenic (CCA). Materials and methods: This study applied four leachability tests on a field-contaminated soil after 48-h washing with ethylenediamine-N,N-disuccinic acid (EDDS), glutamic-N,N-diacetic acid, ethylenediaminetetraacetic acid and humic substances derived from lignite and two other sources. Results and discussion: It was noteworthy that the reduction in the total metal concentrations after soil washing was not predictive of the leaching behaviour. When assessed by toxicity characteristic leaching procedure (TCLP) and waste extraction test (WET), Cu and As leachability was decreased as a result of their extraction by soil washing. By contrast, when assessed by synthetic precipitation leaching procedure (SPLP) and European Council Waste Acceptance Criteria (ECWAC) tests, Cu and As leachability was found to increase, probably because the effect of destabilization of residual metals during soil washing was more observable in unbuffered leaching solutions. On the other hand, Cr leachability was acceptably low in TCLP and WET but still exceeded drinking water standard in SPLP and ECWAC tests. Conclusions: The three chelating agents were able to meet the criteria for Cu in all leachability tests, while the limits of As concentrations could only be met by EDDS in TCLP test. The three humic substances reduced the leachate concentrations of Cu and As without destabilizing the residual metals; however, the reduction was insufficient to meet the required limits in all leachability tests considered. © 2013 Springer-Verlag Berlin Heidelberg.

Hartley N.R.,University of Canterbury | Tsang D.C.W.,University of Canterbury | Tsang D.C.W.,Hong Kong Polytechnic University | Olds W.E.,University of Canterbury | And 2 more authors.
Soil and Sediment Contamination | Year: 2014

Industrial timber treatment sites have resulted in widespread soil contamination by Cu, Cr, and As, presenting potential long-term liability and associated risks to human health and the environment. This study evaluated the roles of natural humic substances (lignite-derived humic substances, standard and commercially available humic acids) and biodegradable chelating agents (ethylenediamine-N,N-disuccinic acid (EDDS) and glutamic-N,N-diacetic acid (GLDA)) for soil washing. Batch kinetic experiments revealed that humic substances promoted Cu extraction at pH 8, but they were significantly adsorbed on the soil at pH 4, possibly posing impediment to soil remediation. The metal extraction by EDDS and GLDA was comparable to that of EDTA (ethylenediamine-tetraacetic acid), and it was more effective at pH 4 than pH 8, probably due to acidic dissolution of metal precipitates and oxides. Metal distribution analysis indicated that the carbonate fraction of Cu and the oxide fraction of As and Cr were mainly extracted, while the exchangeable fraction of Cu increased. The residual leachability tests showed that humic substances reduced the Cu and As leachability but the reduction was insufficient. In contrast, EDDS was able to reduce the leachate concentrations of Cu and As to below 5 mg L-1, meeting the waste acceptance criteria for landfill disposal. Nevertheless, soil washing methods and remediation strategy may need further modifications to facilitate site restoration and promote soil recycling. © 2014 Copyright Taylor and Francis Group, LLC.

Discover hidden collaborations