Spherical Sponge Iron Research Articles

Influence of Reaction Temperature on Nitrate Removal from Water by SSI

Spherical sponge iron (SSI) with high activity and intension could be could be utilized to remove nitrate from wastewater. Influence of reaction temperature on nitrate removal by SSI from wastewater was investigated. Because of erosion battery reaction of SSI in solution, pH in solution increased quickly once SSI was added in and then maintain above 10 despite of nitrate original concentration. The reaction temperature has certain influence under higher nitrate original concentration, while little influence under lower nitrate concentration. It was concluded that nitrate removal by SSI appeared to be the first-order reaction because most of the reaction order was 1. The apparent reaction rate constant of nitrate removal was change slightly with the reaction temperature. It was suggested that the limited key of nitrate reduction by SSI was the diffusion of reactant because the activity energy, which was 11.37 and 7.24kJ/mol, was lower than 30kJ/mol.

Influence of Reduction Agent of SSI on its Cadmium Removal from Wastewater

Spherical sponge iron (SSI) with high activity and intension could be prepared through direct reduction by charcoal or hydrogen. The capability of cadmium removal by SSI was investigated in. It was suggested that the reaction of SSI reduced by hydrogen was higher than that reduced by charcoal, and the increasing rate of pH and cadmium removal in solution by SSI reduced by hydrogen was higher than that reduced by charcoal. Moreover, cadmium removal percentage by SSI reduced with hydrogen was much higher than that reduced by charcoal. When the original concentration of cadmium was 50mg/L, cadmium removal by SSI appeared to be the pseudo-first-order reaction because the reaction order was from 0.861 to 0.984. The apparent reaction rate constant of cadmium removal by SSI reduced with charcoal was 0.586 h-1. While hydrogen was utilized as reduction agent, the apparent reaction rate constant of cadmium removal was increased by 7.3 and 13.7 times.

E-pH Diagram of Fe-N-H<sub>2</sub>O System and its Application in Nitrate Removal from Water by SSI

Spherical sponge iron (SSI) with high activity and intension could be utilized to remove nitrate from wastewater. Reduction product of nitrate by SSI was investigated through static state experiment combined with E-pH diagram of Fe-N-H2O system. In a certain range of pH and redox potential, the speciation of iron include Fe0, Fe2+, Fe3+, Fe(OH)2 and Fe(OH)3, and the speciation of N was NO3-, N2, NH4+, or NH3 as the initial speciation of N was nitrate. pH in solution increased to above 10 in 6min because of quick erosion battery reaction of zero-valent iron in solution. Moreover, the E value in solution declined quickly to the minimum and then increased slightly because of dissolution of oxygen from atmosphere. It was suggested that nitrite was the intermediate product during reduction of nitrate by SSI, and ammonium was the finial product of nitrate and nitrite reduction. Nitrate removal from wastewater was related with escape of ammonia, which was gas state of ammonium in water, when the water solution was alkaline.

Influence of pH on Cadmium Removal from Wastewater by SSI

Spherical sponge iron (SSI) with high activity and intension could be prepared through direct reduction by hydrogen. pH value in solution increased despite initial pH because a large amount of H+ was depleted along with erosion battery reaction of SSI. It was suggested that initial pH has significant influence on pH value in solution and cadmium removal percentage by SSI. When the initial pH maintained at 2.03, cadmium removal percentages were only 10.17% and 22.00%, respectively, in 10min and 30min. While the initial pH was adjusted to 3.00, cadmium removal percentage could be elevated to 73.10% and 95.46% in similar libration time. Cadmium removal by SSI appeared to be the first-order reaction. When the initial pH was maintained at 2.03, the apparent reaction rate constant of cadmium removal by SSI was only 0.434 and 1.027 h-1, while which could be elevated to 5.882 and 5.249 h-1 when the initial pH was adjusted to 3.00.

E-pH Diagram of Fe-N-H<sub>2</sub>O System and its Application in Nitrite

Reduction product of nitrite by Spherical sponge iron (SSI) was investigated through static state experiment combined with E-pH diagram of Fe-N-H2O system. In a certain range of pH and redox potential, the speciation of iron include Fe0, Fe2+, Fe3+, Fe(OH)2 and Fe(OH)3, and the speciation of N was NO2, NO3-, N2, NH4+ or NH3 as the initial speciation of N was nitrite. pH in solution increased to above 10 in 6min because of rapid erosion battery reaction of zero-valent iron. Moreover, the E value in solution declined quickly to the minimum and then increased slightly because of dissolution of oxygen from atmosphere. It was suggested that ammonium was the finial product during the reduction of nitrite by SSI. Nitrite removal from wastewater was related with escape of ammonia, which was gas state of ammonium, when the water solution was alkaline.

Influence of Reduction Temperature of SSI on Nitrate Removal from Wastewater

Spherical sponge iron (SSI) with high activity and intension could be prepared through direct reduction by hydrogen. To optimize the reduction technology of SSI and its removal ability for nitrate from wastewater, the influence of reduction temperature of SSI on nitrate removal was investigated. It was suggested that nitrate removal ability of SSI increased to the summit and then declined with the increasing of reduction temperature. When the reduction temperature of was T4, nitrate removal percentage reached to the maximum. When the original concentration of nitrate was only 5 mg-N/L, the additive quantity of SSI could prove plenty of zero-valent iron in a short time, and reduction temperature of SSI has little influence on nitrate removal. Nitrate removal by SSI appeared to be the pseudo-first-order reaction despite of reduction temperature. While nitrate original concentration was elevated to 50mg-N/L, the reaction order declined to the range of from 0.534 to 0.629 which was closed to 0.5, and the apparent reaction rate constant was 1.411 to 1.773 h-1.

Reduction of SSI by Hydrogen and its Microscopic Morphology

Spherical sponge iron (SSI) with high activity and intension possesses potential characteristics to be utilized as wastewater treatment material, such as higher iron content, uniform particle size, higher compressive strength, etc. Observation on apparent morphology of exterior and microscopic morphology of SSI reduced by hydrogen under different temperature was carried on with SEM. When the reductive temperature was relatively lower than T4, the quantities of iron grain in exterior and interior of SSI increased with the increasing of temperature. When the temperature was elevated to T5, the particle size of iron grain was increased, and lots of macro-holes formed, especially in the interior section of SSI. When the temperature was T4, the SSI possesses more favorable ability to remove pollutant from wastewater. Moreover, the iron content in SSI was mostly reach to the summit under this temperature. In summarization, the reduction temperature should be controlled under T4 temperature if the sponge iron was utilized in wastewater treatment.

Thermodynamics of Spherical Sponge Iron Reduced by Hydrogen

Spherical sponge iron (SSI) with high activity and intension could be prepared through direct reduction by hydrogen. To optimize the reduction technology, thermodynamics of SSI reduction was investigated. Oxygen residue ratio in SSI declined with the reaction time despite of reaction temperature. It was concluded that SSI reduced by hydrogen appeared to be the first-order reaction, and the apparent reaction rate constant k was 0.289 h-1 to 3.819 h-1. Activity energy of SSI reduction was 22.19 kJ•mol-1 and 81.58 kJ•mol-1 corresponding to the lower temperature and higher temperature. When the temperature was lower than T4, the reaction rate was lower. Consequently, the optimized temperature should be controlled more than T5 to elevate the reduction rate.

Influence of Reduction Time on Specific Surface Area of SSI

Spherical sponge iron (SSI) with high activity and intension possesses potential characteristics to be utilized as wastewater treatment material. Influence of reduction time on specific surface area and distribution of different diameter holes were investigated. It was suggested that reductive time has significant influence on the specific surface area of SSI reduced by hydrogen under the optimized temperature. When the reductive time increased from t1 to t3, the porosity increased from 44.32% to 50.62%. While the specific surface area of SSI declined significantly from 3.089 m2/g to 0.307 m2/g when the reductive time increased from t1 to t3. On the other hand, newly formed nucleus should be combined with the adjacent formed one, and larger holes were formed. Consequently, the specific surface area of SSI declined quickly while the reduction time was prolonged, and the mean pore size varied from 275.7nm to 4611.3 nm. To utilize the SSI in wastewater treatment to remove pollutants, t1 was the optimized reductive time for its preparation.

Dynamic Test of Nitrite Removal by SSI from Wastewater

Spherical sponge iron (SSI) with high activity and intension could be prepared through direct reduction by hydrogen. To investigate the optimized method of nitrate removal from wastewater by SSI, dynamic testing of nitrate removal has been investigated. pH values should be elevated quickly after the addition of SSI, and nitrate removal percentage reached to more than 88% during dynamic state experiment. Nitrate removal expressed two-phase removal process including the nitrate removal percentage increasing phase persistently and the nitrate removal percentage maintaining constant phase. The reduction temperature of SSI has significant influence on nitrate removal during fore-period. When the nitrate concentration was 5mg-N/L, nitrate removal percentage could only amount to 60% even the libration time prolonged to 200h. When the nitrate concentration increased to 50mg-N/L, the nitrate removal concentration increased quickly to about 80% and then the removal percentage maintained about 88%.

Kinetic Model of Spherical Sponge Iron Reduced by Hydrogen

Spherical sponge iron (SSI) with high activity and intension could be prepared through direct reduction by hydrogen. To optimize the reduction technology, kinetic model of SSI reduction was established. The total reaction rate changing with reduction index R was deduced which describing the total reaction rate with effective diffusion coefficient De and chemical reaction rate constant k. According to the weight loss curve of SSI reduction, De and k were calculated. The total reactive rate increased with the increasing of temperature because both De and k increased with the increasing of reaction temperature. Compared De with k, it concluded that SSI reduced by hydrogen was controlled by the chemical reaction, combination of the chemical reaction and the internal diffusion, the internal diffusion when the temperature was lower than T3, from T3 to T4, over T5, respectively.

Influence of Reduction Time of SSI on Nitrite Removal from Wastewater

Spherical sponge iron (SSI) with high activity and intension could be prepared through direct reduction by hydrogen. To optimize the reduction technology of SSI and its removal ability for nitrate from wastewater, the influence of reduction time of SSI on nitrate removal percentage was investigated. Because the specific surface area was impact smartly by the reduction time of SSI, it was suggested that nitrate removal ability of SSI should declined with the increasing of reduction time once the reduction time longer than the optimized reduction time. When the reduction time was t1, nitrate removal percentage reached to the maximum. When the nitrate original concentration was 5mg-N/L, the reaction order was closed to 0.7 and the apparent reaction rate constant was 0.323 to 0.359 h-1. When nitrate original concentration increased to 50 mg-N/L, nitrate removal reaction appeared to be the pseudo-first-order reaction, and the apparent reaction rate constant was 0.314 to 0.248 h-1.

Analysis on Reductive Kinetics of SSI Reduced by Hydrogen

Spherical sponge iron (SSI) with high activity and intension could be prepared through direct reduction by hydrogen. To optimize the reduction technology, reductive kinetics of SSI was analyzed on the basement of unreacted core model. In the light of the single reaction surface theory, the ratio of internal diffusion resistance fI and chemical reaction resistance fR was calculated according to the weight loss curve of SSI reduction. Under different temperature, both fI and fR increased with the reaction time, especially the radium of unreacted core was small after a period of reaction time. Compared the ratio of fI and fR, it concluded that SSI reduced by hydrogen was controlled by the chemical reaction, combination of chemical reaction and the internal diffusion, the internal diffusion under the temperature being lower than T3, from T3 to T4, more than T5, respectively.

Influence of Reduction Temperature on Specific Surface Area of SSI

Spherical sponge iron (SSI) with high activity and intension possesses potential characteristics to be utilized as wastewater treatment material. Influence of reductive temperature on specific surface area and distribution of holes with different diameter were investigated. It was suggested that reductive temperature has significant influence on the specific surface area of SSI. When the temperature was controlled at T1 to T5, the porosity was 42.57% to 51.91%. When the temperature was lower than T4, the specific surface area was belonged to the range from 1.867 m2/g and 3.089 m2/g, while which declined sharply to 0.616 m2/g as the temperature increased to T5. When the reductive temperature was lower than T4, mean pore size varied from 275.7 nm to 449.6 nm, while which increased abruptly to 1270 nm as temperature increased T5. To utilize the SSI in wastewater treatment to remove pollutants, T4 was the optimized temperature.

Analysis on Reductive Kinetics of SSI Reduced by Hydrogen

Spherical sponge iron (SSI) with high activity and intension could be prepared through direct reduction by hydrogen. To optimize the reduction technology, reductive kinetics of SSI was analyzed on the basement of unreacted core model. In the light of the single reaction surface theory, the ratio of internal diffusion resistance fI and chemical reaction resistance fR was calculated according to the weight loss curve of SSI reduction. Under different temperature, both fI and fR increased with the reaction time, especially the radium of unreacted core was small after a period of reaction time. Compared the ratio of fI and fR, it concluded that SSI reduced by hydrogen was controlled by the chemical reaction, combination of chemical reaction and the internal diffusion, the internal diffusion under the temperature being lower than T3, from T3 to T4, more than T5, respectively.

Influence of Reduction Temperature on Specific Surface Area of SSI

Spherical sponge iron (SSI) with high activity and intension possesses potential characteristics to be utilized as wastewater treatment material. Influence of reductive temperature on specific surface area and distribution of holes with different diameter were investigated. It was suggested that reductive temperature has significant influence on the specific surface area of SSI. When the temperature was controlled at T1 to T5, the porosity was 42.57% to 51.91%. When the temperature was lower than T4, the specific surface area was belonged to the range from 1.867 m2/g and 3.089 m2/g, while which declined sharply to 0.616 m2/g as the temperature increased to T5. When the reductive temperature was lower than T4, mean pore size varied from 275.7 nm to 449.6 nm, while which increased abruptly to 1270 nm as temperature increased T5. To utilize the SSI in wastewater treatment to remove pollutants, T4 was the optimized temperature.