Characterization of nickel hydroxide sludge using the variable-pressure SEM.

摘要

Acid mine drainage lime treatment sludge is characterized with the variable pressure scanning electron microscope. The major components are shown to be detrital material such as silicates and clay minerals and neutralization products such as gypsum and metal hydroxides.; X-ray mapping and progressive sludge leaching experiments are performed to locate the major nickel bearing species. Progressive leaching was performed for two hours at pH 4, 3.5, and 3. It is observed that there is incomplete nickel extraction for all leach conditions. X-ray mapping establishes that the remaining nickel is due to minor amounts of Ni/S and Ni/O and more significantly colloidal sized nickel-silicon-aluminum complexes; which seem to result from neutralization.; Charge contrast imaging was also considered for characterization. It was studied on the mineral gibbsite to establish optimum working conditions for maximum contrast. Pressure, working distance, bias, scan rate and beam current are varied independently while the specimen current was monitored. Maximum contrast is shown to occur consistently at a specimen current of 3 nA. This implies that the user can operate over a wide range of conditions as long as the specimen current is maintained at its optimum value. This technique is then applied to the analysis of precipitated nickel hydroxides. Charge contrast proved not too informative because the particles are too small. Large electron doses at high magnifications can mask the subtle variation in local charging.