Filtration improvement of zinc sludge by using unconventional alkalization sequence

The novel ways for the filtration improvement of zinc hydroxide sludge precipitated from the zinc\|containing solutions was investigated. It was found that, when the zinc\|containing solutions were added to sodium hydroxide solution, the filtration of the obtained precipitates was improved to some extent, depending on the molar ratios of OH\ -/Zn, in comparison with those obtained by conventional addition of hydroxide solution to zinc\|containing solution, even the ratios were kept the same in these two alkalization methods. The experimental results showed that such an improvement may be contributed to the presence of muddy precipitates formed homogeneously in the sludge. It was suggested that it was zinc\|containing solution that should be added into hydroxide solution, when the zinc was removed from aqueous solution by the precipitation of zinc hydroxides. As a result, the sludge obtained will be filtered and rinsed readily.