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(2004)Journal ArticleInteraction of aqueous Au species with goethite, smectite and kaolinite
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(2003)Journal Article
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(2008)Journal ArticleThe principles of limestone drain systems that are commonly used to passively remediate acid rock drainage have been adapted and modified for remediation of acidic and metal-rich drainage that is produced from broad scale agricultural land use of regions underlain by Acid Sulfate Soils (ASS). The acidic drainage water from sugar cane fields in an ASS catchment was collected from an open drain, filtered to reduce the transport of large particulates, and passed vertically through a polyethylene tank, which was filled with limestone aggregates ( less than or equal 75 mm). This Closed Tank Reactor (CTR) uses the principles of oxic and anoxic limestone drain systems that are designed to increase the partial pressure of carbon dioxide and thereby the alkalinity produced from the dissolution of limestone by metal-laden influent. During a non-continuous 70 day monitoring period, the discharge from the CTR had higher pH, lower acidity and lower metal concentrations compared to the inflow. Under average flow conditions (9 lpm), similar proportions of incoming dissolved aluminium and iron (61% and 56% respectively) were retained within the CTR. Two perforated pipes in the base of the CTR were used to flush precipitates from the system under rapid flow conditions (>50 lpm). The flushing was effective in removing approximately 10% of accumulated iron but only about 0.3% of accumulated aluminium from the CTR. Accumulation of aluminium inside the CTR is likely to present operational problems in attempts to apply such technology to many coastal acid sulfate soil drains. © 2008 Springer Science+Business Media B.V.
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(2008)Journal ArticleAn open limestone channel (OLC) was constructed within an existing drain to treat the acidic and metal-rich drainage waters generated from an acid sulfate soil (ASS) catchment. The OLC was constructed downstream of a catchment pump and it consisted of a series of ponds and limestone sections. The accumulation of sediment over the limestone, preventing contact of limestone with acidic water, was the greatest problem impacting the OLC in its first year of operation. The continuous or sporadic operation of the catchment pump (at 120 l/s) was not sufficient to flush sediment from the limestone. The accumulation of large amounts of sediment onto the limestone reduced the amount of alkalinity and calcium released into solution. However, if the sediment is removed by agitating the limestone then an equivalent or greater amount of alkalinity may be added to solution and more metals removed from solution compared to fresh limestone. The coating on the limestone had a high concentration of manganese oxides in addition to slightly lower concentrations of aluminium and iron. Removal of these metals from the water was due to the increase in pH produced by limestone dissolution in addition to sorption reactions of the existing coating which had natural microbial activity. © 2008 Springer Science+Business Media B.V.
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(2006)Journal Article
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(2006)Journal ArticleThe water quality of drainage discharged via pumping from an acid sulfate soil (ASS) affected catchment used for sugar cane farming is temporally very variable and is influenced by the various rain event magnitudes, their antecedents, and the particular phase of the discharge in any rain event. Rainfall episodes can cause substantial changes in acidity and dissolved metal concentrations in ASS drainage waters over very short time scales with minimum pH often reached within a few hours of initiation of the rainfall event. The initial increase in acidity and dissolved metals concentrations often observed can be attributed mainly to `first flush` effects resulting from mobilization of salts present in the upper soil profile. During the middle of a large rainfall event dilution effects may result in a decrease in concentrations of dissolved species, but increases in acidity and dissolved metals (particularly aluminium) concentrations in the recession portion of the hydrograph often occur as small field drains discharge into main channels. These observations assist both in understanding of the hydrogeochemical processes leading to acid and metals release from acid sulfate soils affected catchments, and in developing appropriate strategies to treat contaminated discharge waters from such catchments. © 2005.
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(2006)Journal ArticleCatchments that contain acid sulfate soils can discharge large quantities of acid and dissolved metals into waterways. At McLeods Creek in far northern NSW, Australia, the acidity from the hydrolysis of dissolved metal species, particularly aluminium and iron, contributes to greater than 70% of the total acidity. Therefore, a poor relationship exists between both calculated and titrated acidity and pH because of the dominant influence of these hydrolyzable metal species. Determination of the so-called `cold acidity` by direct titration with NaOH yields results that are difficult to replicate because of the buffering effects of suspended solids, carbon dioxide ingassing, and/or Mn-II and Fe-II oxidation in the sample as the titration end-point is approached. Samples that are pre-treated with sulfuric acid and hydrogen peroxide produce results ( of `hot acidity`) that can be easily replicated and are similar to calculated acidities based on elemental analysis and speciation calculations. The cold acidity values for titrations of 105 water samples from the chosen field site are often higher than hot acidity values as a result of the loss of carbonate acidity during pre-treatment of samples for hot acidity analysis.
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