Catalytic decomposition of hydrazine nitrate is a very important research topic in the environmental protection field. Herein, we used an Ru/C catalyst for the decomposition of hydrazine nitrate in HNO₃, and the reaction kinetics and mechanism were studied in detail. The kinetics study of the decomposition of hydrazine nitrate (0.01 M) was conducted in the temperature range 313–343 K in 0.1 M HNO₃ in the presence of Ru/C. The apparent activation energy for this reaction was 46.6 kJ mol⁻¹ according to a fitting of the experimental data, while the reaction order was 1.5. It was also found that the reaction pathway of the catalytic decomposition of hydrazine nitrate on the Ru/C catalyst involved two processes: heterogeneous catalytic disproportionation of hydrazine nitrate at the catalyst surface and oxidation of hydrazine nitrate with catalytically generated HNO₂.

An improved apparatus is used for nucleation measurements according to Nielsen's method. A new method is proposed to calculate the dilution ratio N of the reaction solution during nucleation rate determination. With the rule, when the initial apparent supersaturation ratio S’=f(N) in the dilution tank is controlled from 1.3 to 3.0, crystal nucleus dissolving and secondary nucleation can be avoided satisfactorily. Experiments are realized by varying the supersaturation ratio from 15.6 to 93.3 and temperature from 15 °C to 50 °C. Ferrous oxalate is precipitated by mixing equal volumes of ferrous sulfate and oxalic acid solution. The experimental results showed that the nucleation rate of ferrous oxalate in the supersaturation range above is characterized by the primary homogeneous mechanism and can be expressed by the equation R_N = A_Nexp(-E_a/RT)exp[-B/(ln S)²], where A_N = 3.9×10¹³ m⁻³ s⁻¹, E_a = 33.9 kJ mol⁻¹, and B =13.7. The crystal growth rate can be expressed by equation G(t)=k_gexp(-E'_a/RT) (c-c_eq)^g, where k_g = 3.6 × 10¹³ m/s, E'_a = 58.0 kJ mol⁻¹, and g = 2.4.

Two types of nanofiltration membranes were tested to remove uranium dissolved in ammonium nitrate solution, and the influence of operating parameters as transmembrane pressure, tangential velocity and feed temperature was investigated. Experimental results showed NF270 membrane can reject more than 96% uranium and allow most (90% min) ammonium nitrate solution passed by, and with a permeate flux of 60 L/(m²·h). Nanofiltration seems to be a promising technology for the removal of uranium and recovery of ammonium nitrate simultaneously.