Search

In Australia, the assessment of acidity hazard in acid sulfate soils requires the estimation of operationally defined acidity fractions such as actual acidity, potential sulfidic acidity, and retained acidity. Acid--base accounting approaches in Australia use these acidity fractions to estimate the net acidity of acid sulfate soils materials. Retained acidity is the acidity stored in the secondary Fe/Al hydroxy sulfate minerals, such as jarosite, natrojarosite, schwertmannite, and basaluminite. Retained acidity is usually measured as either net acid-soluble sulfur ([S.sub.NAS]) or residual acid soluble sulfur ([S.sub.RAS]). In the present study, contributions of schwertmannite and jarosite to the retained acidity, actual acidity, and potential sulfidic acidity fractions were systematically evaluated using [S.sub.NAS] and [S.sub.RAS] techniques. The data show that schwertmannite contributed considerably to the actual acidity fraction and that it does not contribute solely to the retained acidity fraction as has been previously conceptualised. As a consequence, [S.sub.NAS] values greatly underestimated the schwertmannite content. For soil samples in which jarosite is the only mineral present, a better estimate of the addedjarosite content can be obtained by using a correction factor of 2 to [S.sub.NAS] values to account for the observed 50-60% recovery. Further work on a broader range of jarosite samples is needed to determine whether this correction factor has broad applicability. The [S.sub.RAS] was unable to reliably quantify either the schwertmannite or the jarosite content and, therefore, is not suitable for quantification of the retained acidity fraction. Potential sulfidic acidity in acid sulfate soils is conceptually derived from reduced inorganic sulfur minerals and has been estimated by the peroxide oxidation approach, which is used to derive the [S.sub.RAS] values. However, both schwertmannite and jarosite contributed to the peroxide-oxidisable sulfur fraction, implying a major potential interference by those two minerals to the determination of potential sulfidic acidity in acid sulfate soils through the peroxide oxidation approach., Introduction Over 500000 [km.sup.2] of acid sulfate soils (ASS) are found globally, mainly in highly populated, coastal plains (Sullivan et al. 2012). In Australia, nearly 215 000 [km.sup.2] of land [...]

Author(s): Eileen Sproat Emison [1, 4]; Andrew S. McCallion [1, 4]; Carl S. Kashuk [1]; Richard T. Bush [1]; Elizabeth Grice [1]; Shin Lin [1]; Matthew E. Portnoy [2]; David [...]

Substantial marcasite and pyrite were recently identified in the upper-most unoxidised Holocene clay-peat sediments at Bungawalbin Swamp, a coastal backswamp on the Richmond River floodplain, north-east New South Wales, Australia. Marcasite (Fe[S.sub.2]), the mineral dimorph of pyrite, is considered a rare secondary mineral in estuarine sediments and its abundance at Bungawalbin Swamp is highly unusual. The morphology and distribution of marcasite in the sulfidic sedimentary profile was examined and compared with the palynological record. Marcasite, recognised by its distinctive platy morphology and disulfide composition, occurred exclusively within organic remnants in only the upper most 1 m of the sulfidic sediment layer. Pyrite occurred throughout the sulfidic profile. A dramatic change in the sedimentary conditions at Bungawalbin Swamp from a marine environment, characterised by the presence of avicenniaceae (i.e. mangrove), to a fresh-brackish environment correlates directly with the occurrence of marcasite. The occurrence of substantial marcasite may provide a valuable environmental proxy of fresh-brackish depositional swamp environments. Additional keywords: iron sulfide, pyrite, acid sulfate soil, sulfidic., Introduction Marcasite is the mineral dimorph of pyrite, sharing the same chemical composition of Fe[S.sub.2]. Diagenic pyrite is common in marine and estuarine sediments (Berner 1970), whereas diagenic marcasite has [...]

The observations presented in this paper illustrate that significant amounts of monosulfidic black oozes (MBO) were eroded from flood mitigation drainage canals and redistributed across a coastal floodplain during a flood event associated with extreme deoxygenation and a massive fish kill. MBO are organic materials enriched in iron monosulfides and thick layers can accumulate in drains affected by acid sulfate soils. Laboratory studies have demonstrated that MBO can react rapidly when brought into suspension to completely consume dissolved oxygen. The abundance of MBO in flood mitigation drains and their extreme reactivity implicated MBO in the acute deoxygenation of the Richmond River, north-eastern New South Wales, Australia, following a major flood in February 2001. The field observations of MBO redistribution provide valuable evidence to help explain how these materials may interact and contribute to the deoxygenation of floodwaters. Additional keywords: iron sulfides, pyrite, monosulfides, acid volatile sulfur, deoxygenation, MBO., Introduction Monosulfidic black oozes (MBO) are organic materials enriched in iron monosulfides. Thick layers of MBO accumulate in many canals that drain acid sulfate soil (ASS) landscapes (Bush et al. [...]

Organic oozes enriched in iron monosulfides are called monosulfidic black ooze (MBO). The occurrence and abundance of MBO were quantified in natural tributaries and man-made drainage canals on a typical coastal river floodplain. Thick deposits of MBO occurred in drains and the protected upper reaches of tributaries in acid sulfate soil (ASS) areas. Acid-tolerant lilies grew prolifically in these areas, contributing large amounts of decaying organic debris. The MBO contained up to 6.3% acid-volatile sulfur (equivalent to 18% iron monosulfide), an order of magnitude greater than reported previously for natural sediments. It also contained up to 6% pyritic sulfur (equivalent to approximately 11% pyrite). Sulfate and iron from surrounding ASS combined with abundant organic matter and protected flow in ASS drains provide excellent conditions for sulfate reduction, leading to iron sulfide precipitation and the accumulation of organic detritus. When mixed with water, the iron monosulfide in MBO can react within minutes to completely consume dissolved oxygen. There are thousands of drains in ASS areas that may have thick deposits of MBO. The MBO has the potential to cause rapid and severe effects on water quality. The challenge is to develop management practices that reduce the formation and accumulation of MBO in acid sulfate landscapes. Additional keywords: pyrite, iron sulfides, de-oxygenation, water quality., Introduction Organic oozes enriched in iron monosulfides are called monosulfidic black ooze (MBO). The reduction of organic matter by sulfate-reducing bacteria in these sediments produces hydrogen sulfide (H2S), which reacts [...]

Four acid sulfate soil (ASS) materials were subjected to anoxia after varying periods of oxidation to determine the geochemical response of these types of soils to flooding. The response of the partially oxidised ASS materials to the exclusion of oxygen was variable. The rate of sulfide oxidation, acidification, and the production of soluble oxidation products such as sulfate, iron, and aluminium generally decreased markedly when subjected to anoxia. However, especially in the highly acidic ASS materials (i.e. pH Additional keywords: soil acidification, pyrite oxidation, pyrite re-formation, chromium reducible sulfur, reduction, soil incubation., Introduction Acid sulfate soils (ASS) contain iron sulfides (principally pyrite) or the products of sulfide oxidation (White and Melville 1996). Unoxidised sulfidic materials are often referred to as potential ASS. [...]

The potential environmental hazard of acid sulfate soil (ASS) materials is directly related to both the net acidity and the rate that actual acidity is released from these soil materials into the environment. While current environmental hazard assessment techniques for ASS materials are able to quantify the net acidity, they do not take account of differences in the rate of sulfide oxidation (the dominant source of actual acidity) and differences in the rate of acidification. In this study the rate of sulfide oxidation during incubation was examined for 4 ASS materials. The effect of pH and oxygen availability on the rate of sulfide oxidation was assessed. The ASS materials were incubated in: (i) gauze where oxygen diffusion was not restricted, and (ii) sealed 100-µm-thick plastic bags which greatly limited oxygen diffusion. When oxygen diffusion was not restricted, an accelerated oxidation of sulfide occurred when the pH decreased below pH 4.0. The accelerated rate of sulfide oxidation at such low pH did not occur when oxygen diffusion was limited. This study indicates that the initial pH of an ASS material is a useful additional indicator of the potential environmental hazard of an ASS material when oxygen is expected to be non-limiting, such as when ASS materials are excavated and stockpiled. The recommended action criteria need to be reassessed, as the data indicate that the current criteria are conservative for alkaline and neutral ASS materials, but should be lowered for all acidic ASS materials (i.e. pH Additional keywords: pyrite oxidation, acidification, chromium reducible sulfur, soil incubation., Introduction The potential environmental hazard associated with acid sulfate soil (ASS) materials often results from the interaction between the net acidity, largely derived from sulfide oxidation, and the rate this [...]

Acid sulfate soil (ASS) materials that are subject to oxidation are often treated with neutralising agents to minimise the export of acidity that may result from pyrite oxidation. The effects of additions of both CaC[O.sub.3] and seawater-neutralised bauxite refinery residue (SNBRR) on the oxidation of sulfides and acidification were assessed for 4 ASS materials using laboratory incubation experiments. As the application of sub-optimal rates of neutralising materials can occur for a variety of reasons, the effect of application rates were also examined. Two application rates were chosen; a sub-optimal rate [approximately 20% of the theoretical neutralising requirement (NR)] and an excessive application rate (>250% of the NR). There was minimal sulfide oxidation and no acidification after the addition of excess CaC[O.sub.3] over the 180 days of incubation. The addition of excess SNBRR prevented acidification, but substantial sulfide oxidation still occurred. Following a brief initial increase in pH when sub-optimal rates of CaC[O.sub.3] and SNBRR were applied, the treated ASS materials rapidly acidified. For three of the ASS materials the addition of sub-optimal amounts of CaC[O.sub.3] had little impact on the rate of sulfide oxidation. However, for the other ASS material (a peat) both the rates of sulfide oxidation and acidification were accelerated by the addition of sub-optimal rates of CaC[O.sub.3], resulting in higher soluble Fe and Al concentrations than in the untreated ASS materials. For some of the ASS materials, sub-optimal applications of SNBRR resulted in elevated soluble Al. Additional keywords: pyrite oxidation, lime, chromium reducible sulfur, marcasite., Introduction The presence of acid sulfate soils (ASS) is a major constraint on land use and development in coastal areas of Australia (White and Melville 1996). ASS contain iron sulfides [...]

The reduced inorganic sulfur fraction of 4 acid sulfate soil (ASS) materials was quantified using a variety of peroxide oxidation procedures. The temperature and duration of the peroxide oxidation were found to markedly affect the peroxide oxidisable sulfur determination. For 3 ASS materials with low total carbon content (i.e. Additional keywords: pyritic sulfur, peroxide oxidisable sulfur, chromium reducible sulfur, jarosite, sulfur budget., Introduction It is important to have an accurate and reliable measure of the reduced inorganic sulfur (generally assumed to be pyrite) content of acid sulfate soil (ASS) materials to avoid [...]

Total sulfidic acidity (TSA) and total potential acidity (TPA) are derived from peroxide oxidation of acid sulfate soil materials (ASS), and are measures of the sulfidic acidity and the net acidity (net acidity = sulfidic acidity + actual acidity - acid neutralising capacity), respectively. The TSA and TPA of 4 ASS materials were determined using a variety of peroxide oxidation procedures and compared with the sulfidic acidity and net acidity derived from the use of an acid-base accounting model. TSA and TPA values both varied greatly with each peroxide oxidation method used, and both measures were found to substantially underestimate (i.e. by 23-85%) both sulfidic acidity (as determined from the chromium reducible sulfur content) and net acidity (as determined by acid-base accounting). A major cause of this underestimation of acidity was the retention of acidity through the precipitation of jarosite during peroxide oxidation. Substantial clay mineral dissolution appears to have occurred during peroxide oxidation of the ASS materials, as indicated by increased soluble aluminium. Such dissolution may contribute to the underestimation of both sulfidic and net acidity for the ASS materials using peroxide oxidation methods. The loss of acidity to the atmosphere was identified as a possible additional interference. This study shows the peroxide oxidation methods examined here are subject to substantial interferences, which caused large underestimations of acidity, and consequently, are unable to reliably provide accurate measurements of sulfidic and net acidity in ASS materials. Additional keywords: pyritic sulfur, total potential acidity, total sulfidic acidity, net acidity, jarosite, acid budget, acid neutralising capacity., Introduction The acid released upon the oxidation of pyrite in acid sulfate soils (ASS) can severely reduce water quality and may cause adverse effects to aquatic life, reduced crop production, [...]