Clarification of black ammonium polyphosphate liquids-recycling of byproduct tops

摘要

The process allows essentially all of the nitrogen and P2O5 values in the treated black ammonium polyphosphate liquid to be recovered in the form of valuable clarified product. In the process, a heel of black liquid fertilizer is first clarified by a prior-art procedure using flocculants. The improvement over the prior art picks up with the byproduct tops which is then diluted with the water of formulation required to dissolve additional amounts of ammonium polyphosphate melt. This diluted liquid is filtered, the filter cake containing upwards of 99 percent of the undesirable black carbonaceous material is discarded, and the clear filtrate, which contains essentially all of the nitrogen and P2O5 originally in the tops, is then used in lieu of the prior-art water of formulation to dissolve additional ammonium polyphosphate melt to produce more black ammonium polyphosphate liquid.