We get lumps when Ca(OH)2 reacts with NH4Cl to form NH4OH and it cannot be filtered easily .Any idea?

Question

In the process of manufacturing Ammonium vanadate,we need to get rid of water pollution due to Ammonical Nitrogen from NH4Cl.We can afford using Ca(OH)2 instead of NaOH.We get lumps and cannot filter them to get NH4OH from the lumpy slurry.This does not happen when we use NaOH. The wastewater contains NH4Cl alongwith 0.3% impurities of Al and Mg. The problem is only with 85% pure hydrated lime. There is no problem with 48%NaOH. But it is uneconomical.We do not understand this. Gels should form with NaOH as well as with Ca(OH)2. This causes filteration problems.Any idea to avoid sudden growth of particle size and lump formation with use of lime.

Answer 1

The other byproducts of your reaction are NaCl from NaOH and CaCl2 from Ca(OH)2. NaCl is highly soluble, but CaCl2 is not. It seems the filters are serving their purpose.You could try a centrifuge, a cyclone or a settling tank to reduce the number of times the filters must be cleaned.