I have not actually tried it but have seen customers using this process.
This process had also been recommended by a DTC supplier.

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.

The magnesium hydroxides pH is buffered, so overdosing is not a
problem as compared to using sodium hydroxide. Magnesium hydroxide
slurry could also block metering pump and freeze easily. The cost of both
DTC and/or magnesium hydroxides are higher than using sodium
hydroxide. The sludge volume may be less than that using sodium
hydroxide. DTC sludge is toxic due to the carbamate in the formulation.

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