Selection of permeable reactive barrier materials for treating acidic groundwater in acid sulphate soil terrains based on laboratory column tests

The Shoalhaven region of NSW experiences environmental acidification due to acid sulphate soils (ASS). In order to trial an environmental engineering solution to groundwater remediation involving a permeable reactive barrier (PRB), comprehensive site characterisation and laboratory-based batch and column tests of reactive materials were conducted. The PRB is designed to perform in situ remediation of the acidic groundwater (pH 3) that is generated in ASS. Twenty-five alkaline reactive materials have been tested for suitability for the barrier, with an emphasis on waste materials, including waste concrete, limestone, calcite-bearing zeolitic breccia, blast furnace slag and oyster shells. Following three phases of batch tests, two waste materials (waste concrete and oyster shells) were chosen for column tests that simulate flow conditions through the barrier and using acidic water from the field site (pH 3). Both waste materials successfully treated with the acidic water, for example, after 300 pore volumes, the oyster shells still neutralised the water (pH 7).     

Changes in geochemistry and mineralogy of thermally altered coal, Upper Hunter Valley, Australia

Igneous intrusions thermally and geochemically alter coal, commonly causing economic and safety problems for many coal mines. The effects of two dykes on the inorganic content of the Late Permian bituminous Upper Wynn seam were determined from analyses of 44 samples that were collected along transects approaching the intrusions. Petrographic and XRD data were used to determine sample mineralogy, and INAA and XRF spectrometry were utilised to determine the contents of 57 elements. The mineralogy of the unaltered coal, altered coal and dyke is dominated by carbonates, particularly dawsonite, which formed by epigenetic precipitation at a late stage, after thermal alteration. Ankerite and siderite are the products of thermal alteration and are restricted to the altered coal and dykes.Principal component analysis, correlations and compositional trends approaching the intrusions were used to subdivide the elements into groups and to identify the mineralogical affinity of each group. Geochemical data are more sensitive than mineralogy for defining the size of the alteration halo, and three zones ranging from unaltered coal, through altered coal to highly coked coal are recognised as each intrusion is approached.The alteration halos differ in extent (9.5 and 56 m wide), but their size is not a multiple of the size of the causative intrusion. At the contact between coal and intrusion, concentrations of elements with affinities to some aluminosilicates, oxides, carbonates, sulphides and organic components are enriched, while other aluminosilicate-related elements are depleted. In the altered coal towards the edge of the alteration halo, some aluminosilicate elements are enriched and oxide elements are depleted.     

Influence of localised igneous activity on cleat dawsonite formation in Late Permian coal measures, Upper Hunter Valley, Australia

Stable (δ¹³C and δ¹⁸O) and radiogenic ⁸⁷Sr/⁸⁶Sr isotopic data have been used to investigate the origin of cleat dawsonite (NaAlCO₃(OH)₂) in the Late Permian Wittingham Coal Measures of the Upper Hunter region in the Sydney Basin, New South Wales. The δ¹³C_PDB values have a narrow range (− 1.7‰ to + 2.4‰), with an average of + 0.3‰, suggesting a magmatic source for the carbon. In contrast, δ¹⁸O_SMOW values have a wide range (+ 13.6‰ to + 19.8‰), and decrease systematically with decreasing distance from a major intrusion. This systematic variation reflects establishment of localised hydrothermal cells. Water–rock interaction between fluids associated with these hydrothermal cells, and Rb-poor volcaniclastic detritus in the coal measures, produced mantle-like ⁸⁷Sr/⁸⁶Sr (0.705032 to 0.706464) in the dawsonite.