Search

On exposure to carbon dioxide (CO2) at a pressure of 3 bars, compacts formed from pressed ground slag, and 12.5 weight percent water, were found to react with approximately 18% of their own weight of CO2. The reaction product formed was calcium carbonate causing the slag to self-cement. Unconfined compressive strengths of 9MPa were recorded in carbonated compacts whereas strengths of1 MPa were recorded in non-carbonated slag compacts. As molten stainless steel slag containing dicalcium silicate (C2S) cools it can undergo several phase transitions. The final transformation from the beta-polymorph to gamma-C2S is accompanied by a volume change that causes the slag to self-pulverise or 'dust'. As a consequence of this the fine grained portion of the slag contains more of this phase whilst the coarser particles of the slag contain more of the calcium magnesium silicates that contribute the bulk of the waste. The fine fraction (125 microm) of the slag when ground is found to react to the same extent as the ground bulk slag and produces compacts with equivalent strength. A coarser fraction (4-8 mm) when ground to a similar grading does not react as extensively and produces a weaker product. Additions of ordinary Portland cement (OPC) at 5 and 10 percent by weight did not alter the degree of reaction during carbonation of the bulk slag or ground fine fraction, however the strength of the 4-8 mm fraction was increased by this change.

The acid neutralisation capacity test is widely used to assess the long‐term performance of waste materials prior to disposal. Samples of fixed mass are exposed to increasing additions of nitric acid in sealed containers and the resultant pH is plotted as a titration curve. In this work, the acid neutralisation capacity test was used in the assessment of an accelerated carbonated stainless steel slag. Difficulties arose in applying the test procedure to this material. This was largely because of the raised pressure from significant volumes of released carbon dioxide trapped in the sealed sample containers, causing an alteration to leachate pH values. Consequently, the acid neutralisation capacity test was modified to enable testing of samples in equilibrium with the atmosphere. No adverse effects on the results from testing of a carbonate free material were recorded

Concentrations of total mercury (T-Hg) were measured in eel and roach from five selected rivers in East Anglia, U.K, to determine Hg bioaccumulation in fish throughout the region. Levels of T-Hg in sediment and river water were also analysed to assess their potential as pathways to the fish. Accumulated Hg levels in River Yare eel and roach continue to exhibit a strong positive relationship with surface sediment Hg levels, which are declining with time. Mercury in muscle from all sampled fish were below the limit set by the EU Directive (93/351/EEC). Analysis of muscle:liver (M:L) ratios confirm that eel from all sites are in equilibrium with their environment. Various statistical methods (single factor analysis of variance, Spearman's correlation coefficients) were performed on the experimentally derived data on mercury concentrations in fish flesh. Significant correlations were noted for accumulated Hg in fish flesh with length and weight in eel, and length, weight and age in roach.

Bulk deposition and soils were analysed for total mercury (T-Hg) from five sites in East Anglia, U.K., in order to evaluate atmospheric deposition as a source of Hg to the region, and to determine whether Hg in soils constitutes a source of Hg to fish. Levels of Cr, Cu, Ni, Pb and Zn were also measured in soils to determine the strength of association with Hg. Average mercury concentrations in soils were 0.135 mg kg−1 and were above the previously reported UK average of 0.098 mg kg−1. All sites revealed an increasing north to south gradient of anthropogenic heavy metal loading to surface soils with enhanced loading for Hg, Cu, Pb, and Zn at the River Yare location. Levels of T-Hg in bulk deposition displayed a similar gradient, averaging 89 ng l−1 for the region, suggesting atmospheric deposition as a likely source of Hg to soils and biota (fish) in East Anglia.

Partitioning of metals between dissolved and particulate sedimentary phases provides useful information which can be used to assess their mobility and sources. Bioavailability and toxicity has also been found in many cases to be related to metal partitioning. Sediment cores were taken from salt marsh areas in the Thames Estuary and along the Essex and North Norfolk coasts, and porewaters were separated by centrifugation and filtration. Concentrations of Cd, Cu, Fe, Mn, Ni and Pb in the porewaters, and in HCl/HNO3 digests of the total sediment, were determined by AAS. The order of metal mobility showed inter-site differences, indicating that the partitioning characteristics were influenced by physico-chemical and hydrodynamic controls. These inter-site differences were reflected in the partitioning distribution of Mn and the sediment redox potentials. Cadmium showed the strongest tendency to partition towards dissolved phases, and porewater concentrations decreased in the Essex salt marshes with increasing...

Mercury mobilization off of aquifer sediments by acid rain, road salt runoff and fertilizer solutions is investigated using column and batch equilibria experiments. Sediments from the Kirkwood Cohansey aquifer System, New Jersey are used to determine the mobilization potential of mercury due to changing infiltration water chemistry. In a series of batch equilibria and column experiments mercury contaminated sediments were treated with a dilute nitric acid solutions, 20-20-20 fertilizer, super phosphate fertilizer and dilute sodium chloride solutions. Mercury mobilization is enhanced by solutions containing sodium chloride and 20-20-20 fertilizer. These solutions can remove up to 90% of the mercury sorbed to the sediments. Mercury mobilization by phosphate fertilizer and acid rain proceeds at a slower rate and only 30% of the mercury is removed. It was found that irrigation of the sediments following treatment with 20-20-20 fertilizer or sodium chloride increased mercury mobilization associated with the de...