The Effect Of Some Environmental Factosrs On The Photolysis Of Nitrate And Its Mechanism

Nitrogen is one of the important elements in agricultural production. The lower utilization rate of nitrogen fertilizer is a common problem confronted in the world. In the study of nitrogen loss, the mechanism of nitrogen loss was not clear at present. With the development of photochemistry and understanding of activity of nitrate, the issue of the nitrogen loss caused by photodegradation of nitrate is attracting more attentions.In this paper, the environmental factors on photodegradation of nitrate were researched, such as pH, concentration, Fe²⁺, NH₄⁺ along with their mechanism of conversion. The results showed as follows:1.Under the condition of the dark, degradation of nitrate did not occur in 4h. The same result got in the solution added the Fe²⁺and NH₄⁺.2.Degradation rate of 2mg/L nitrate was 17.28% after 4h under UV irradiation and it became constant with the prolongation of irradiation time. When Fe²⁺and NH₄⁺ was added in the solution, degradation rate of nitrate became constant 3h later.3.The pH had a remarkable influence on photolysis of nitrate. From pH 4.0 to 9.0, degradation rate of 0.5 mg/L nitrate ranged from 8.8% to 39%, and from 6.68% to 20.7%, respectively. The photodegradation rate became constant while the pH value is increased continuously and the formation rate of nitrite showed the same trend.4.Fe²⁺ had a remarkable influence on photolysis of nitrate. The degradation rate of nitrate increased with the total concentration of the Fe²⁺ increasing. In 0.5mg/L nitrate solution added 0.2mmol/L FeSO₄, degradation rate of nitrate varied from 35.43% to 55.12%. In 0.5mg/L nitrate solution added 0.2mmol/L FeSO₄·(NH₄)₂SO₄, degradation rate of nitrate was 45.56%. The degradation rate of nitrate increased when the content of FeSO₄·(NH₄)₂SO₄ raised continuously, which was higher than the treatment received same level of Fe²⁺.5.It showed that photodegradation of nitrate kinetics followed the first-order equation. The constant of the reaction rate was in inverse proportion to the concentration of nitrate at pH 8.0. 6. NH₄⁺ was not detected during the process of photolysis of nitrate. According to the principle of mass conservation, it is possible that nitrate was ultimately transformed into other forms. The percentage of N was less than 8% in the nitrate solution and increased under the presence of Fe²⁺ and NH₄⁺, which probably related to intermediate of Fe²⁺ and NH₄⁺ during the processes of photolysis of nitrate.