Betriebserfahrungen mit Aluminiumnitrat (AN)

Aluminum salts are being utilized in the water treatment technology (water-, waste water-, process water purification, etc.) in order to coagulate, precipitate and flocculate dissolved and undissolved substances present in water. Among other products, the pulp and paper industry uses aluminum compounds (primarily PAC and aluminum sulfate) for the process water treatment fibre recovery, drainage acceleration on the paper machine, anionic trash removal, as well as for sizing and retention aids. Apart from the well-known positive characteristics of aluminum, the anions such as chlorides and sulfates are, however, responsible for various disadvantageous reactions like corrosion, formation of hydrogen sulfide, anaerobic odor emission, salt accumulation in the white water system, deposition of calcium sulfate and precipitation of metal sulfides associated with a declining brightness of the stock. Preserving the positive aspects of PAC and aluminum sulfate applications, the abovementioned disadvantages can, to a certain magnitude, be reduced or even eliminated through a back up of chloride or sulfate anions by nitrate. Due to a more favorable redox potential persisting in an anaerobic environment, contrary to the oxygen in sulfate, the oxygen bound in nitrate (NO - 3 ) preferentially provides a source of oxygen for bacteria. Without generating toxic, corrosive and odor emissions of sulfur compounds (H 2 S), being the fact for sulfate, the chemical conversion of nitrate results in elementary, non-poisonous and inert nitrogen (N 2 ), as found at 78 % in air. This presentation outlines some practical experiences gained from product applications at both Haindl Schongau mill and Augsburg mill, which illuminate possibilities for the utilization of aluminum nitrate and poly aluminum nitrate respectively, accentuating its positive characteristics. Heiko Hilbert developed the application of aluminum nitrate and poly aluminum nitrate for the pulp and paper industry in 1994. He applied for patent in 2000.