Ferric alums reduction

This energetic reducing agent can be maintained at constant strength in aqueous hydrochloric acid solution for a reasonable period. It is advisable, however, to re-standardise it after 24 hours standing. It serves for the reduction of aromatic nitro compounds, some nitroso bodies, many azo dyes, and of nearly all the dyes which yield leuco-compounds. It is easily standardised against a ferric salt—say ferric alum—using potassium thiocyanate as indicator. From the equations —... 

Chemical precipitation is used in porcelain enameling to precipitate dissolved metals and phosphates. Chemical precipitation can be utilized to permit removal of metal ions such as iron, lead, tin, copper, zinc, cadmium, aluminum, mercury, manganese, cobalt, antimony, arsenic, beryllium, molybdenum, and trivalent chromium. Removal efficiency can approach 100% for the reduction of heavy metal ions. Porcelain enameling plants commonly use lime, caustic, and carbonate for chemical precipitation and pH adjustment. Coagulants used in the industry include alum, ferric chloride, ferric sulfate, and polymers.10-12... 

The charge on the suspended solids is often sufficiently negative to yield a stable dispersion that settles slowly and is difficult to filter. In this case, the key to effective colloid removal by sedimentation is reduction of the zeta potential to zero or near-zero. Once the charge is reduced or eliminated, electrostatic repulsive forces are minimized. The gentle agitation of the flocculation basin then causes numerous colloid collisions, first with formation of microflocs and then with visible floe particles, which can easily be settled or filtered. Coagulants such as alum, ferric chloride or cationic polymers all function primarily as charge reducers [4,41,42]. 

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