Browsing by Subject "Zinc"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Restricted
    Modelling zinc heap bioleaching
    (Elsevier, 2007) Petersen, J; Dixon, D G
    A comprehensive modelling study of the HydroZinc™ heap bioleach process, using the HeapSim modelling tool, is described. The model was calibrated on the basis of a small number of column leach experiments and compared against pilot heap test results. The model calibration thus confirmed, a detailed sensitivity study was conducted in order to establish the key parameters that determine the overall rate of Zn extraction. In the present case these were found to be oxygen gas–liquid mass transfer, various factors affecting the delivery of acid into the heap, and factors affecting the temperature distribution within the heap. A set of improved design parameters are proposed that would almost double the zinc conversion rate measured in the pilot plant – from 83% in 740 days to 78% in 383 days – and increase zinc production rate from 1.77 to 4.35 kg/m2/day. However, this improvement must be evaluated in the context of various implications for the downstream process.
  • Thumbnail Image
    Item
    Open Access
    Plasma vitamin A and zinc levels in HIV-infected adults in Cape Town, South Africa
    (2003) Visser, M E; Maartens, G; Kossew, G; Hussey, G D
    A cross-sectional study of 132 adults attending an HIV clinic in Cape Town, South Africa, was conducted to determine predictors of low plasma vitamin A and Zn levels. No patients were on antiretroviral therapy. The possible confounding effect of the acute-phase response was controlled by including C-reactive protein levels in multivariate analysis and by excluding active opportunistic infections. Retinol levels were low (< 1.05 μmol/l) in 39% of patients with early disease (WHO clinical stages I and II) compared with 48 and 79 % of patients with WHO stage III and IV respectively (P<0.01). Plasma Zn levels were low (< 10.7 μmol/l) in 20% of patients with early disease v. 36 and 45 % with stage III and IV disease respectively (P< 0.05). C-reactive protein levels were normal in 63 % of subjects. Weak, positive associations were found between CD4+lymphocyte count and plasma levels of retinol (r 0.27; 95 % CI 0.1, 0.43) and Zn (r 0.31; 95% CI 0.25, 0.46). Multivariate analysis showed the following independent predictors of low retinol levels: WHO stage IV (odds ratio 3.4; 95 % CI 2.1, 5.7) and body weight (odds ratio per 5 kg decrease 1.15; 95% CI, 1-08, 1.25), while only body weight was significantly associated with low Zn levels (OR per 5 kg decrease 1.19; 95% CI 1.09, 1.30). CD4+lymphocyte count <200/μl was not significantly associated with either low retinol or Zn levels. In resource-poor settings, simple clinical features (advanced disease and/or weight loss) are associated with lowered blood concentrations of vitamin A and/or Zn. The clinical significance of low plasma retinol and/or Zn levels is unclear and more research is required to establish the role of multiple micronutrient intervention strategies in HIV disease.