R. John Morrison

Sequential extraction procedures for the determination of phosphorus forms in sediment

This article summarizes the main extraction methods for sedimentary phosphorus (P) determination. With sequential chemical extractions, P is supposed to be selectively removed from different compounds in the sediments. Extraction schemes using strong acids and alkaline solutions have been tested on different sediments and found not to extract well-defined fractions. In addition, several systematic errors in these schemes have been detected. Thus, these schemes have been modified and simplified accordingly. The Standards Measurements and Testing Program of the European Commission (SMT) method is a popular modification of these extraction schemes, as it is simple to handle, allows laboratories to achieve reproducible results and could provide a useful tool for routine use by water managers. The SEDEX (sequential extraction method) method, another popular modification, is widely applied in biogeochemical research as it can separate authigenic carbonate fluorapatite from fluorapatite. Other chemical extractions using chelating compounds have attempted to extract P bound with iron and calcium in sediments without disturbing clay-bound or organic P, the purpose being to determine the algal-available non-apatite, apatite and organic fractions of sediment P. All extraction procedures still yield operationally defined fractions and cannot be used for identification of discrete P compounds. Future modifications of the extraction scheme should aim to achieve better extraction efficiency and selectivity, simple handling techniques and methods that can prevent the extracted P from being re-adsorbed onto Fe(OOH) and CaCO3.

Fire intensity drives post-fire temporal pattern of soil carbon accumulation in Australian fire-prone forests

The impact of fire on global C cycles is considerable but complex. Nevertheless, studies on patterns of soil C accumulation following fires of differing intensity over time are lacking. Our study utilised 15 locations last burnt by prescribed fire (inferred low intensity) and 18 locations last burnt by wildfire (inferred high intensity), with time since fire (TSF) up to 43years, in a homogenous forest type in south eastern Australia. Following a stratified approach to mineral soil sampling, the soil % total C (% CTot) and % recalcitrant pyrogenic C (% RPC), were estimated. Generalised additive models indicated increases in % CTot at TSF >30years in sites last burnt by wildfire. Estimates in sites last subjected to prescribed fire however, remained constant across the TSF chronosequence. There was no significant difference in % CTot between the different fire types for the first 20years after fire. In the first 10years after wildfires, % RPC was elevated, declining to a minimum at ca. TSF 25years. After prescribed fires, % RPC was unaffected by TSF. Differences in response of % CTot and % RPC to fire type may reflect the strength of stimulation of early successional processes and extent of charring. The divergent response to fire type in % CTot was apparent at TSF longer than the landscape average fire return interval (i.e., 15 to 20years). Thus, any attempt to increase C sequestration in soils would require long-term exclusion of fire. Conversely, increased fire frequency is likely to have negligible impact on soil C stocks in these forests. Further investigation of the effects of fire frequency, fire intensity combinations and interaction of fire with other disturbances will enhance prediction of the likely impact of imposed or climatically induced changes to fire regimes on soil C.

Soil carbon in Australian fire-prone forests determined by climate more than fire regimes

Knowledge of global C cycle implications from changes to fire regime and climate are of growing importance. Studies on the role of the fire regime in combination with climate change on soil C pools are lacking. We used Bayesian modelling to estimate the soil % total C (% CTot) and % recalcitrant pyrogenic C (% RPC) from field samples collected using a stratified sampling approach. These observations were derived from the following scenarios: 1. Three fire frequencies across three distinctive climate regions in a homogeneous dry sclerophyll forest in south-eastern Australia over four decades. 2. The effects of different fire intensity combinations from successive wildfires. We found climate had a stronger effect than fire frequency on the size of the estimated mineral soil C pool. The largest soil C pool was estimated to occur under a wet and cold (WC) climate, via presumed effects of high precipitation, an adequate growing season temperature (i.e. resulting in relatively high NPP) and winter conditions sufficiently cold to retard seasonal soil respiration rates. The smallest soil C pool was estimated in forests with lower precipitation but warmer mean annual temperature (MAT). The lower precipitation and higher temperature was likely to have retarded NPP and litter decomposition rates but may have had little effect on relative soil respiration. Small effects associated with fire frequency were found, but both their magnitude and direction were climate dependent. There was an increase in soil C associated with a low intensity fire being followed by a high intensity fire. For both fire frequency and intensity the response of % RPC mirrored that of % CTot: i.e. it was effectively a constant across all combinations of climate and fire regimes sampled.

Sinter Plant Operations: Hazardous Emissions

This article presents an outline of the iron ore sintering process, which introduces the blast furnace slag-forming requirements to allow an understanding of the required adjustments to flux addition in the sintering process; some basic concepts of the sintering reactions are also introduced. The recovery of miscellaneous wastes using high S, N, Cl content materials in sinter plants has been associated with some hazardous emissions, such as dust, NOx, SOx, and dioxins. The formation mechanism of these hazardous pollutants and some practical countermeasures are discussed.

Sinter Plant Operations: Raw Materials

The raw materials for an integrated steelworks can be classified into four categories, which are iron ores, fluxes, fuels, and reverts. The characteristics of these raw materials strongly affect the metallurgical properties of iron ore sinter and sinter plant performance. An optimal ore blend design is therefore essential to produce low cost and high quality hot metal. Without doubt, some hazardous components are brought into the production process, and therefore, there are some associated pollutants. A good preparation of raw materials is the first step for in-process anti-pollution action. This chapter will introduce the common materials used in iron ore sintering and the handling procedures in an integrated steelworks.

Oxygen exchange during the reaction of POCl3 and water

To investigate O exchange during the reaction of POCl3 and water, natural abundance POCl3 was reacted with water highly enriched in 18O, and the resulting H3PO4 was isolated as KH2PO4. This reaction was conducted with and without tetrahydrofuran (THF) as a solvent, and was controlled in THF and violent in its absence. Approximately 5 × 10–4 M aqueous solutions of the KH2PO4 were analyzed using electrospray ionization mass spectrometry, to estimate the proportions of the mass-clumped 16,17,18O isotope analogues of [H2PO4]–. During analysis, ~29 % of [H2PO4]– dehydrated to [PO3]–, for which the proportions of the O isotope analogues were also measured. These proportions were compared with those predicted for O exchange at either four or three positions on the P atom of POCl3. The data strongly support O exchange at all four positions, whether or not THF was used to moderate conditions during the reaction. This result clears the way for safe, predictable synthesis of heavy-O labelled orthophosphate from POCl3 and 18O enriched water for evaluation as an environmental and biochemical tracer.