：This paper inquired into possibility of production of powder active carbon with wheat straw by phosphoric acid method and its optimum process conditions.

Twice technology reforms and the structure of main equipment for the recovery of chromic acid sludge by phosphoric acid method are described.

Study on recovery iodine from wet-process phosphoric acid by solvent flotation;

Study on the decolorization of wet-process phosphoric acid with activated carbon;

Extraction system of purifying wet-process phosphoric acid with solvent extraction method;

Then hydrochloric acid method,kiln method and wet-process phosphoric acid(WPA) were introduced.

Phosphoric acid production was introduced,including production method,development and direction of thermal-process phosphoric acid.

For the excessive P_2O_5 in the offgas discharged from thermal-process phosphoric acid production in a plant,as well as the actual conditions in the plant,the offgas quantity and excess air ratio in the offgas system are calculated,and the operating conditions are analyzed.

Study on production of potassium ammonium phosphate with wetprocess phosphoric acid;