In message Tat Choo  writes
>Basically the magnesium hydroxide (mixed in a tank with mixer, or
>supplied in a slurry form) is meter into the settling tank that contains the
>pre-reacted metal bearing DTC floc, and the sludge is supposed to settle
>much faster than if using DTC alone. The process is also commonly used
>with waste water having high concentration of organic such as
>stripper/developer or surfactant bearing cleaner solutions. High organic
>create sludge that is difficult to settle. The magnesium hydroxide also
>help to increase the density in the sludge and create a sludge that
>dewatered faster. This decreases the chance of getting wet cakes from
>filter press.
We use Lime or Calcium Hydroxide in slurry form to neutralise to ph 8.5
after acid cracking and before adding floc. The lime aids settling
considerably and improved our treatment 100% when we switched from using
Caustic solution. I don't know how much Magnesium Hydroxide is but it
sounds more expensive than lime.
Regards 
Paul Gould

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