Condensation of extractive phosphoric acids based on the Al2O3, Fe2O3 and MgO-contg. phosphorites was carried out in a glass reactor placed inside a tubular vertical furnace. The heated reactor allowed for condensation of acids at 200-300 degrees C and dehydration times 45-135 min. The increasing content of pollutants resulted in a decrease of polyphosphate content in products. The presence of Al ions resulted in a decrease of the condensation in the highest extent. The increase in condensation temp. and dehydration time resulted in an increase of polyphosphate fraction content in products, but the temp. effect was higher than those of the dehydration time.