In general I would agree with Mr. Miller.  We switched to Mg hydroxide 
     on all our batch treatment processes here.  It is MUCH more cost 
     effective that sodium hydroxide simply due to its alkaline content 
     pound-for-pound.  Magnesium hydroxide improves solids settling.  You 
     do not have to worry about over shooting pH either which can happen 
     very easily with sodium hydroxide if it is being added manually.
     
     We continue to use sodium hydroxide in our continuous waste water 
     treatment system because of the ease of use issues mentioned below as 
     well as kinetics.  Magnesium takes longer to react because it is in a 
     solid slurry and as the dissolved OH is consumed additional particles 
     of MgOH  must dissolve.  We had to purchase a special mixing drum pump 
     tube from Lutz that allows us to mix the slurry before we pump it for 
     use in a batch treatment procedure.
     
     Michael Holan
     Process Engineer
     Continental Circuits Corp. of Texas


______________________________ Reply Separator _________________________________
Subject: Re: Mag. hydroxide & DTC in waste water
Author:  "Richard R. Miller" <[log in to unmask]> at INTERNET
Date:    4/25/97 12:11 AM


Mg hydroxide is primarily utilized to increase "weight" to the solids formed, 
thereby improving the settling characteristics of "over-loaded" systems. 
     
There are products on the market that combine Mg with DTC, or other heavy ions, 
to achieve this same affect.
     
A more cost effective, and easier approach, would be to utilize 
"solids-recycling" from your sludge holding tank to your primary reaction tank. 
This will provide, the "weight", to improve your settling, as well as, reduce 
your DTC, flocculant, and alkalinity requirements by 20-50%. Also, this will 
allow you to use sodium hydroxide, in place of, Mg, or Ca Hydroxide (cost/ease 
of use savings).
     
     
Rick Miller
     
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