Solid Energy New Zealand Ltd.

Christchurch, New Zealand

Solid Energy New Zealand Ltd.

Christchurch, New Zealand
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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.

Olds W.E.,O'Kane Consultants NZ Ltd | Weber P.A.,O'Kane Consultants NZ Ltd | Pizey M.H.,Solid Energy New Zealand Ltd | Pope J.,CRL Energy Ltd.
New Zealand Journal of Geology and Geophysics | Year: 2016

The Reddale Coal Mine is located within the Brunner Coal Measures, which are often assumed to be potentially acid-forming rocks that will release acidity when disturbed by mining. The pre-mining assessment of the site acid mine drainage (AMD) potential assumed overburden acid-neutralising capacity was negligible, similar to Brunner Coal Measures in other areas, and that AMD would occur almost immediately. Column trials using poorly stored and partially oxidised drill core indicated potentially acid-forming (PAF) overburden readily produced acidity with no lag period. Based on the pre-mining assessment, a Ca(OH)2 dosing plant was constructed for AMD management. Once mining commenced, tiphead samples collected during construction of the Ferndale engineered landform showed that the net acid-producing potential of the potentially acid-forming overburden was overestimated by about one-third when acid-neutralising capacity and non-sulphide forms of sulphur were accounted for. When coupled with material properties which resulted in good compaction of waste rock, construction of the engineered landform in 4 m lifts to minimise convective oxygen flux and aglime (<2.5 mm CaCO3) amendments to each lift, acidity loads from the Ferndale engineered landform were negligible. Compliance monitoring downstream of the mine site at Red4 shows that, to date, site discharge pH has remained circum-neutral. Pre-mining AMD management decisions, primarily construction of a Ca(OH)2 dosing plant that was never commissioned, therefore proved overly conservative. The timing and expense of AMD management has the potential to influence project feasibility and needs to be well understood. © 2016 The Royal Society of New Zealand.

Boyer S.,Lincoln University at Christchurch | Wratten S.,Lincoln University at Christchurch | Pizey M.,Solid Energy New Zealand Ltd | Weber P.,Solid Energy New Zealand Ltd
Pedobiologia | Year: 2011

As key 'ecosystem engineers', earthworms improve mineralization of organic matter, plant growth, soil quality, and are an important component of many terrestrial food webs. Under appropriate conditions, they are therefore likely to accelerate the restoration of soil ecosystem function after mining.Conserving naturally occurring populations and facilitating their recolonisation appears as the most efficient way to increase earthworms' overall effect. The impact of mining activities and restoration measures on New Zealand endemic earthworm communities was tested. Earthworm biomass and diversity were compared in four different habitat types.Mining activities, not surprisingly, are shown here to have a detrimental impact on earthworm communities. Soil stockpiling induces anaerobic conditions at and below a depth of 1. m, where earthworms do not survive. The use of stockpiled soil for vegetation replanting therefore leads to low diversity and low abundance of earthworms. An alternative restoration technique consisting in transferring vegetation and soil units (the vegetation direct transfer) was efficient in preserving earthworm populations with earthworm biomass and diversity not significantly different from those observed in undisturbed areas. Based on these results, we recommend vegetation direct transfer (VDT) to be prioritised whenever it is logistically and economically feasible. When VDT is not applicable, low stockpiles should be prioritised as they will comprise a higher proportion of good quality soil (at the surface) and a lower proportion of anaerobic and compacted soil (below 1. m depth at the studied site). © 2011 Elsevier GmbH.

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.

Davies H.,University of Otago | Weber P.,Solid Energy New Zealand Ltd. | Lindsay P.,Solid Energy New Zealand Ltd. | Craw D.,University of Otago | Pope J.,CRL Energy Ltd.
Science of the Total Environment | Year: 2011

The Stockton coal mine lies at 700-1100. m above sea level in a mountainous orographic precipitation zone on the West Coast of the South Island of New Zealand. Rainfall exceeds 6000. mm/year and arrives with frequent flood events that can deliver > 200 mm/day. Streams vary in discharges by up to two orders of magnitude over a time scale of hours. Pyritic waste rock at the mine interacts chemically with even the most intense rainfall, and almost all runoff is acidic to some degree. In the most intense rain event recorded in this study (> 10 mm/hour), dilution of acid mine drainage (AMD) occurred and pH rose from 3 to > 5 over several hours, with stream discharge at a monitoring point rising from <0.5 to > 100 cumecs. However, most rain events of similar magnitude are less intense, longer duration, and only raise AMD pH to ~. 4 with similar high discharges. Results presented here for Stockton confirm that it is the intensity of rain events on the hourly scale, rather than the total amount of rainwater delivered to the site, that governs the amount and composition of AMD generated during flood events. Stream discharge loads of dissolved iron and aluminium range from ~. 20 to 1000. kg/hour. Dissolved sulfate and acidity loads are typically ~. 500. kg/hour but can exceed 20. tonnes/hour in rain events.First flush effects observable elsewhere around the world involving peak metal loads following dry periods or seasonal changes are not obvious at Stockton due to the high and variable rainfall environment. Dissolved Fe concentrations may be limited in runoff waters by precipitation of jarosite and schwertmannite, especially when rainfall is sufficiently intense to raise pH to 4 or higher. These minerals are widespread in the exposed waste rock on site. Likewise, precipitation of alunite may occur as pH rises in rain events, but no field evidence for this has been observed. © 2011 Elsevier B.V.

McCauley C.A.,University of Canterbury | O'Sullivan A.D.,University of Canterbury | Weber P.A.,Solid Energy New Zealand Ltd | Trumm D.,CRL Energy Ltd.
New Zealand Journal of Geology and Geophysics | Year: 2010

Thirteen acid mine drainage seeps emanating from waste rock dumps and associated sediment ponds were monitored at Stockton Coal Mine near Westport, New Zealand to identify and quantify metal loads and delineate their spatial and temporal variability. Dissolved metal concentrations ranged from 0.05-1430 mg/L Fe, 0.200-627 mg/L Al, 0.0024-0.594 mg/L Cu, 0.0052-4.21 mg/L Ni, 0.019-18.8 mg/L Zn, <0.00005-0.0232 mg/L Cd, 0.0007-0.0028 mg/L Pb, <0.001-0.154 mg/L As and 0.103-29.3 mg/L Mn and the pH ranged from 2.04-4.31. Currently this acid mine drainage is treated further downstream by a number of water treatment plants employing a combination of ultra fine limestone and Ca(OH)2. However, in the interest of assessing more cost-effective technologies, biogeochemical reactors were assessed in the laboratory as potential cost-effective passive treatment options. Results of mesocosm-scale treatability tests showed that biogeochemical reactors incorporating mussel shells, pine bark, wood fragments (post peel) and compost increased pH to >6.7 and sequestered >98.2% of the metal load from the Manchester Seep located within the Mangatini Catchment. Laboratory results demonstrated that the maximum loading rate was 0.8 mol total metals/m3 substrate, and an average of 20.0 kg/day (7.30 tonnes/year) of metals could be removed by appropriately sized biogeochemical reactors. © 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

Davies H.,University of Otago | Weber P.,Solid Energy New Zealand Ltd. | Lindsay P.,Solid Energy New Zealand Ltd. | Craw D.,University of Otago | And 2 more authors.
Applied Geochemistry | Year: 2011

The Mangatini Stream drains a coal mining area in the mountains of northwestern South Island of New Zealand. Abundant rainfall on pyritic rocks yields acid mine drainage (AMD) to the stream, which flows through a steep gorge at discharges that rapidly increase from <1 to >100m3/s during frequent rain events. The AMD is treated with finely ground limestone, which is discharged as a slurry at a point in the middle of the gorge. The limestone slurry mixes and reacts with the AMD during flow ∼4km downstream over ∼12h. Neutralisation reactions increase stream pH from near 3 (untreated Mangatini Stream water impacted by AMD) to 5-6 in the first 250m downstream, although mixing is commonly incomplete in this zone. Large stream discharge volumes in rain events dilute the neutralising material input, thus driving the pH back towards 4 downstream of treatment. More complete neutralisation is achieved 4km downstream, even in major rain events, and pH can rise to >7. Partial neutralisation is sufficient to remove most of the dissolved Fe(III) (typically ∼30mg/L) from the Mangatini Stream in the first 10m, and remaining dissolved Fe is essentially all Fe(II), which decreases over time as it oxidises and precipitates. Dissolved Al in the Mangatini Stream (typically ∼50mg/L) decreases steadily downstream over ∼100m in the limestone mixing zone. Precipitated Fe and Al form amorphous oxyhydroxides that are transported as suspended solids and deposited on the stream bed with excess limestone in zones of low flow velocity. Dissolved Zn is removed from solution by adsorption to Fe oxyhydroxide when pH reaches ∼5, but dissolved Ni remains in solution despite the neutralisation process. Gypsum precipitation occurs throughout the limestone mixing zone, resulting in at least 30% decrease in dissolved SO42- Minor ettringite forms in the first 100m, but then probably redissolves. The limestone dosing system is an effective method of neutralising the effects of AMD and removing most dissolved metals in a steep mountain stream with frequent rain events where this dynamic environment places many constraints on treatment options. © 2011 Elsevier Ltd.

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