Low-Temperature Carbothermic Reduction of Indonesia Nickel Lateritic Ore with Sub-Bituminous Coal
In this work, the experiment was conducted to investigate the effect of temperature and sub-bituminous coal on upgrading nickel laterites ores by carbothermic reduction. The reduction was carried out in the muffle furnace at a temperature ranging of 800-1100 °C. The produced calcine from reduction step was grounded in vibrating mill, mixed with water and passed on a magnetic separator to separate nickel concentrates from the tailing. The experimental results showed that the concentrate with highest nickel grade was produced at temperature 1000 °C. The nickel grade on concentrate was 5.0 %, with the recovery of nickel was 80.6 %.
Effect of sulfur on the mineral phases of laterite ores at high temperature reduction
Recovery of nickel and cobalt from nickel laterites processed according to the Caron process is hampered by reduction of iron in limonite ores and formation of fosterite in saprolite ores. The Caron process involves the reduction of the ores at temperatures between 700 and 800 °C followed by ammoniacal leaching. The presence of sulfur has been found to markedly improve the Ni and Co recoveries from laterite ores. In this study, limonite and saprolite laterite ores were reduced in the presence of an activator, in the form of elemental sulfur. The mineral phases resulting from the reduction, both in the presence and absence of sulfur were related to recoveries and selectivity obtained from laboratory reduction and leaching tests. The mineral phases were examined using X-ray diffraction with a synchrotron radiation source. The role of sulfur and the history of reduction in effecting the increase in recovery and selectivity of nickel and cobalt was investigated in this study.
High-frequency hearing thresholds: effects of age, occupational ultrasound and noise exposure
AbstractPurpose
It has been suggested that high-frequency audiometry (HFA) could represent a useful preventive measure in exposed workers. The aim was to investigate the effects of age, ultrasound and noise on high-frequency hearing thresholds.MethodsWe tested 24 industrial ultrasound-exposed subjects, 113 industrial noise-exposed subjects and 148 non-exposed subjects. Each subject was tested with both conventional-frequency (0.125–8 kHz) and high-frequency (9–18 kHz) audiometry.ResultsThe hearing threshold at high frequency deteriorated as a function of age, especially in subjects more than 30 years old. The ultrasound-exposed subjects had significantly higher hearing thresholds than the non-exposed ones at the high frequencies, being greatest from 10 to 14 kHz. This hearing loss was already significantly evident in subjects with exposure <5 years and increased with years of exposure and advancing age. The noise exposure group had significantly higher hearing thresholds than the non-exposed group at the conventional frequencies 4 and 6 kHz and at the high frequency of 14 kHz. After stratification for age, there was a significant difference between the two groups at 9–10 and 14–15 kHz only for those under 30 years of age.ConclusionMultivariate analysis indicated that age was the primary predictor, and noise and ultrasound exposure the secondary predictors of hearing thresholds in the high-frequency range. The results suggest that HFA could be useful in the early diagnosis of noise-induced hearing loss in younger groups of workers (under 30 years of age).
