In situ neutralisation of uncarbonated bauxite residue mud by cross layer leaching with carbonated bauxite residue mud.

Unameliorated residue mud from the Bayer process generates highly alkaline leachates (pH ca. 13) after deposition in storage areas. Pre-deposition treatment of bauxite residue mud (BRM) with CO(2) gas (carbonation) lowers leachate pH to ca. 10.5. Laboratory scale leaching columns were used to investigate the potential for in situ pH reduction in existing uncarbonated BRM deposits through exposure to carbonated mud leachate. Leachates from uncarbonated and carbonated residues in single and dual-layer column configurations were analysed for pH, electrical conductivity, carbonate and bicarbonate content, and element concentrations. Air-dried solids were analysed by X-ray diffraction before and after leaching. Cross layer leaching lowers leachate pH from uncarbonated BRM. Leachate pH was significantly lower in dual layer and carbonated residue than in uncarbonated residue between one and 400 pore volumes leached. Carbonated residue porewater as well as dawsonite and calcite dissolution were identified as sources of (bi-)carbonate. Leachate concentrations of As, Cr, Cu, Ga and La were immediately reduced in dual layer treatments compared with uncarbonated residue. No element analysed exhibited a significantly higher leachate concentration in dual layer treatments than the highest observed concentration in single layer treatments. The implementation of dual layer leaching in the field therefore presents an opportunity to improve leachate quality from existing uncarbonated residue deposits and justifies further testing at field scale.

Computed tomographic colonography (CTC) performance: one-year clinical follow-up.

AIM: Computed tomographic colonography (CTC) represents a valuable advance in imaging technology for patients with colonic symptoms who are unfit for or fail to complete investigation with conventional techniques of colonoscopy or barium enema. The aim of this study was to examine whether CTC was sufficient to exclude colorectal cancer in such a population. As our patients were unfit for or unable to complete conventional investigations, we used 1 year clinical follow-up to exclude colonic malignancy. MATERIALS AND METHODS: CTC examination was performed using multi-slice CT in patients fitting pre-determined criteria. All patients who had completed 12 months of follow-up after CTC were included. Data were extracted from patient records and lack of presentation within the 12 months following a negative CTC was assumed to equate to lack of colorectal cancer at initial investigation. RESULTS: One hundred and twelve patients underwent CTC with a median age of 78 years (range 39-95) and median follow-up of 18 months (range 12-26). CTC detected 7 colorectal cancers, with 3 false positives and 1 false negative, giving a sensitivity of 87.5% and specificity of 97.1% for the detection of colorectal cancer. CONCLUSIONS: CTC is a good imaging tool for the exclusion of colorectal cancer in a population unfit for or unable to complete colonoscopy or barium enema, with reasonable sensitivity and specificity for detection of colorectal cancer. However, the optimum investigative strategy for fitter symptomatic individuals is still debated and should be clarified by the results of ongoing randomised controlled trials.

Desorption kinetics of arsenate from kaolinite as influenced by pH.

Arsenic is highly toxic and therefore represents a potential threat to the environment and human health. The mobility and bioavailability of arsenic in soil is mostly controlled by adsorption and desorption reactions. Even though adsorption and traditional batch desorption experiments provide information about the environmental fate of As, the equilibrium conditions imposed in these studies would usually not be reached in the natural environment. Flow-through desorption techniques, where the desorbed species are removed from the substrate, can therefore be used to provide information about the rate and mechanisms of As desorption. The effect of pH on As adsorption reactions is relatively well understood; however, desorption of As and the effect of pH on As desorption remain unexplored. Desorption of As(V) (the most dominant arsenic species in aerated soils) was therefore investigated using batch and flow-through desorption experiments. Traditional batch desorption experiments underestimated the desorption rate of As(V) from kaolinite. The pH had a large effect on the amount of As(V) desorbed from kaolinite, with both an increase and a decrease in pH (from the initial pH 6.4) enhancing As(V) desorption. Modeling desorption over time revealed that the pH can influence As(V) desorption over extended periods of time.

Abnormal neurophysiology in patients with oesophageal motility disorders.

BACKGROUND: The pathology of oesophageal motility disorders is poorly understood. Oesophageal manometry provides only a descriptive assessment of luminal pressure changes. This study applied the investigative methods of the neurophysiologist to gain insight into the pathophysiology of these disorders. METHODS: Twelve healthy volunteers and 28 patients with oesophageal motility disorders underwent oesophageal manometry and balloon stimulation studies. Cortical evoked potentials (CEPs) in response to electrical stimulation of the oesophagus and oesophageal motor evoked potentials (MEPs) to transcranial magnetic stimulation of the cerebral cortex were recorded. RESULTS: Only two patients had abnormalities with a primary defect in muscle function. Fifteen had abnormal responses to balloon stimulation with normal CEPs and MEPs, suggesting a defect in the intrinsic nerves of the oesophagus. Five with achalasia did not respond to balloon stimulation and had abnormal CEPs and MEPs, suggesting widespread neural defects. The remainder had a variety of abnormal responses suggesting possible defects in receptor sensitivity, central processing or sensory neuropathy. There was no correlation between the manometric diagnosis and abnormal neurophysiology, except in patients with achalasia. CONCLUSION: Neurophysiological testing suggests that oesophageal motility disorders are most commonly due to a variety of neural defects.

The cost effectiveness of metal oesophageal stenting in malignant disease compared with conventional therapy.

Expanding metal oesophageal stents are being used more commonly to palliate patients with inoperable oesophageal carcinoma. Many reports have so far documented their clinical effectiveness, however, their high acquisition cost has caused on-going concern when compared with the cost of conventional therapies. We reviewed 64 consecutive patients with inoperable oesophageal carcinoma, half of whom had received our conventional method of palliation using a variety of techniques including, BICAP diathermy, alcohol injection and Atkinson tube insertion. The other half (32 patients) were treated with expandable metal stents -- Gianturco Z stents (Cook UK Ltd) and uncovered Ultraflex stents (Microvasive, Boston Scientific). The physical amount of resources consumed were identified and measured (number of diagnostic and support procedures, days as in patients, number of day cases or outpatient attending) and an average NHS cost was applied to this resource use. All costs were summated over the period of palliation from the date of the first intervention with palliative intent until death. Although the patients in this study were not randomized, the two groups were matched to ensure comparability in clinical manifestation (uncomplicated biopsy proven oesophageal carcinoma) and the average age of patients from each group. A difference was identified between the length of survival in both patient groups and the analysis was corrected for this by estimating a cost per day of palliative support. Patients palliated with metal stents underwent fewer procedures and spent fewer days in hospital during the time period from presentation until death even when corrected for differences in survival. Patient outcome (effectiveness of palliation) was measured by recording mean dysphagia scores which were recorded before and after palliation. Metal stents were found to lead to a significantly higher improvement in dysphagia in comparison to conventional therapy. In addition, the mortality related to metal oesophageal stents was lower than Atkinson tube insertion. The average cost of palliation was much lower in the metal stent group (mean = pound sterling 2817) compared with the cost in those palliated conventionally (mean = pound sterling 4566). However, once this was corrected for survival the difference in the cost of palliation on a per diem basis was reduced (metal stents = pound sterling 60 per day, conventional group = pound sterling 72 per day). The results of our study indicate that the initial high cost of metal stents is more than outweighed by resource savings elsewhere in the hospital by virtue of reduced need for re-intervention and shorter length of hospital in patient stay. Such cost savings taken in combination with the improved clinical effectiveness and low mortality related to metal stents provide significant support for introducing their use into clinical practice.

Dysphagia due to secondary achalasia as an early manifestation of squamous cell carcinoma.

A 59-year-old man, a smoker, presented with features of airflow obstruction due to squamous cell carcinoma of central airways mimicking chronic obstructive airways disease. He also had pronounced dysphagia. Computed tomographic and magnetic resonance imaging scans showed mediastinal tumour invasion but no direct oesophageal involvement. Oesophageal manometry studies revealed that dysphagia was due to the oesophageal motility disorder, secondary achalasia.