Limonite coal-based oxidation-reduction roasting system and method
By designing a limonite coal-based oxidation-reduction roasting system for oxidation and reduction roasting in segments, the problem of difficult atmosphere control and unstable production in the existing process is solved, and a more efficient and stable roasting process is achieved, and product quality and production efficiency are improved.
Patent Information
- Application Number
- CN202410965393.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-07-18
- Publication Date
- 2025-06-20
AI Technical Summary
The existing coal-based reduction and roasting process is difficult to control in the rotary kiln, resulting in partial reoxidation of materials, liquefaction of low-melting materials, rings, local combustion and overfired, and production is unstable and the index is poor.
A coal-based oxidation-reduction roasting system of limonite is designed, including a sequentially connected oxidation roasting system, a reduction roasting system, a cooling pulping system and a hot air circulation system. The oxidation and baking system realizes preheating and oxidation of materials through a dosing feeder and a rotary kiln. The reduction and baking system realizes the reduction of materials through a first screw feeder, a reducing agent bin and an internal spiral reactor. The cooling and pulping system realizes the cooling and pulping of materials through a sealed stirring tank and a spray water system. The hot air circulation system realizes the recycling of hot air through a water bath dust collector and a return air fan.
By oxidizing and reducing roasting in sections, the atmosphere is stable, and partial reoxidation and overburning of the material is avoided, and production stability and index quality are improved. The internal spiral design of the reduction reactor and the use of the hot air circulation system improve the reduction efficiency and energy efficiency and reduce operating costs.
Smart Images
Figure CN120174192A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of metal mineral beneficiation and reduction roasting, and more specifically, relates to a limonite coal-based oxidation-reduction roasting system and method. Background Art
[0002] At present, the coal-based reduction roasting process mainly uses a rotary kiln for roasting. A burner is arranged at the head of the rotary kiln for heating the materials in the rotary kiln. The materials to be roasted are fed into the rotary kiln from the tail after adding pulverized coal in proportion. Theoretically, the reduction roasting is completed through two technological sections of preheating and reduction. However, in actual production, when a single rotary kiln is used for magnetization reduction roasting, the production is unstable, the indexes are poor, and the production line is mostly in a stagnant state. The main reasons for the failure of this process include the following aspects: (1) Reduction and heating are carried out in one rotary kiln. The head of the kiln is in an oxidizing atmosphere, and the middle and tail of the kiln are in a reducing atmosphere. The air passes through the cavity from the head to the tail of the kiln, and the atmosphere is difficult to control. Moreover, the reduced materials are partially re-oxidized after passing through the oxidizing atmosphere at the head of the kiln; (2) In a reducing atmosphere, the low-melting-point substances in the materials to be roasted and pulverized coal are prone to liquefy and form rings; (3) Due to the difficult control of the atmosphere in the kiln, local combustion occurs, the temperature is too high, and over-roasting phenomenon exists; (4) The temperature of the materials in the rotary kiln fluctuates greatly, and the reduction time of the materials cannot be guaranteed at the effective reduction temperature. Summary of the Invention
[0003] The purpose of the present invention is to provide a limonite coal-based oxidation-reduction roasting system and method. The purpose of the present invention is achieved by the following technical solutions: A limonite coal-based oxidation-reduction roasting system of the present invention is characterized in that it includes an oxidation roasting system, a reduction roasting system, a cooling and pulping system, and a hot air circulation system connected in sequence. The oxidation roasting system includes a metering feeder, a rotary kiln, and a burner. The discharge port of the metering feeder is connected to the feed port of the rotary kiln, and the burner is arranged at the head of the rotary kiln. The reduction roasting system includes a first screw feeder, a reductant bin, a reductant screw feeder, a reduction reactor, a discharge chute, a second screw feeder, and a feed chute. The first screw feeder is arranged at the bottom of the head of the rotary kiln, and the feed port of the first screw feeder is connected to the discharge port of the rotary kiln. The reductant screw feeder is arranged at the upper side of the first screw feeder, and the feed port of the reductant screw feeder is connected to the reductant bin. The discharge ports of the first screw feeder and the reductant screw feeder are both connected to the feed port of the reduction reactor through a chute. One end of the second screw feeder is connected to the discharge port of the reduction reactor through a discharge chute, and the other end is connected to the feed chute. The cooling pulping system comprises a sealed stirring tank, a slurry pump and a spray water system. The spray water system is provided in the sealed stirring tank. The feed chute is connected to the feed port of the sealed stirring tank and inserted into the sealed stirring tank. The slurry pump is connected to the lower discharge port of the sealed stirring tank. The hot air circulation system includes a water bath dust collector, a return air fan and an air transmission pipeline. One end of the exhaust pipe of the cooling pulping system passes through the top cover of the sealed stirring tank and is connected to the sealed stirring tank, and the other end is connected to the air inlet of the water bath dust collector. One end of the return air fan is connected to the air outlet of the water bath dust collector, and the other end is connected to the exhaust pipeline. The end of the exhaust pipeline is connected to the kiln head of the rotary kiln and is arranged at the upper end of the burner of the oxidation roasting system.
[0004] Preferably, a flue gas treatment system is also provided at the kiln tail of the rotary kiln, and the flue gas treatment system comprises a hot air exhaust duct, a bag filter and a main exhaust fan.
[0005] Preferably, the exhaust pipe end is arranged 100 mm above the burner of the oxidation roasting system. Preferably, the reduction reactor is an internal spiral reactor, including a driving device, a cylinder, a stirring main shaft, a spiral blade arranged on the outside of the stirring main shaft and a sealing mechanism, a lifting plate is arranged at intervals on the side of the spiral blade, a feed port for entry and an input port for passing the reducing agent are arranged at the top of the reduction reactor, a discharge chute for discharging is arranged at the right end of the reduction reactor, and a temperature sensor is also arranged on the chute.
[0006] A method for oxidizing and reducing roasting of limonite coal-based according to the present invention is implemented by the above-mentioned oxidizing and reducing roasting system of limonite coal-based, characterized in that it comprises the following steps: Step 1 Oxidation roasting operation The limonite is fed into the feed port of the rotary kiln by a quantitative feeder, and heated by spraying fire into the kiln body through a burner. The limonite is dried, preheated, and calcined in the rotary kiln, and the material is heated to 680℃-800℃ to achieve preheating, oxidation, and roasting of the material; the hot flue gas generated in the rotary kiln is discharged to the flue gas treatment system through the hot air exhaust pipe, bag dust collector, and main exhaust fan; Step 2: Reduction roasting operation After oxidation and roasting, the limonite is fed into the reduction reactor from the outlet of the rotary kiln through the first screw feeder. The reducing agent is an oxygenator, calcium hydroxide and coal powder, which are mixed in proportion by a wet method. The reducing agent forms a CO reducing atmosphere inside the reduction reactor. The reduction reactor adopts an internal spiral reactor. The rotation of the internal spiral ensures the full mixing of the reducing agent and the material, and controls the residence time of the material in the cylinder to be 30 - 60 minutes. The designed residence time is determined according to laboratory tests. The lifting plates on the spiral blades lift the material to the highest point of the spiral, which is conducive to the full reaction of the material with the reducing gas, and the oxidized ore is reduced to magnetite; Step 3: Cooling and pulping operation The reduced magnetite is fed into the sealed stirring tank through the discharge chute. The spray water system in the sealed stirring tank directly hydrates the material and stirs it to mix into a pulp with a concentration of 40%, and then it is transported to the subsequent grinding and separation operation system through the slurry pump 32; Step 4: Hot air circulation operation After the excess flue gas in the reduction reactor passes through the first water bath in the sealed stirring tank, it is dusted for the first time. Then, after the dust and water vapor in the flue gas are purified for the second time by the water bath dust collector, it is transported to the kiln head of the rotary kiln by the return air fan for waste gas combustion. The dust-containing slurry in the water bath dust collector returns to the stirring tank to form a closed loop.
[0007] Step 4: Hot air circulation operation After the excess flue gas in the reduction reactor passes through the first water bath in the sealed stirring tank, the dust and water vapor in the flue gas are purified by the water bath dust collector, and then it is transported to the burner for combustion treatment by the return air fan. The dust-containing slurry in the water bath dust collector returns to the stirring tank to form a closed loop.
[0008] Preferably, the iron grade of the limonite is 35 - 55%, the particle size is -3 mm, the pulverized coal is 40% powder of -200 mesh, the calorific value is 6500 kcal, the volatile matter is 28%, the ash content is 24%, and the fixed carbon is 65%.
[0009] Preferably, the reducing agent is composed of an oxygen enhancer, calcium hydroxide and pulverized coal, and the weight parts of the three raw materials are: 7 parts of coal, 2.5 parts of oxygen enhancer, and 0.5 part of calcium hydroxide.
[0010] Preferably, the temperature of the pulp in the cooling and pulping operation in Step 3 is controlled at ≤60 °C.
[0011] Preferably, the oxygen enhancer is any one or a combination of calcium hypochlorite, sodium percarbonate, peroxyamide, calcium peroxide, hydrogen peroxide or ammonium peroxydisulfate.
[0012] The advantages of the present invention are: 1) The coal-based oxidation and reduction roasting are carried out in segments according to the process requirements without interference; 2) In the reduction roasting operation, by adding an oxygen enhancer to the reducing agent, the anaerobic reaction of the coal can be controlled, ensuring the stability of the atmosphere in the reduction roasting operation; 3) The reduction reactor adopts an internal spiral reactor, which is easy to seal, ensures a certain pressure in the reactor, and improves the reduction efficiency. The spiral rotation speed of the reactor is adjustable, and the reduction time can be adjusted according to the reaction requirements. Description of the Drawings
[0013] Figure 1 It is a schematic diagram of the coal-based oxidative reduction roasting process and equipment of the exemplary embodiment of the present invention.
[0014] Figure 2 It is a schematic diagram of the reactor structure.
[0015] Figure 3 It is a schematic diagram of the internal spiral.
[0016] Description of the Reference Numerals 11 - Quantitative feeder, 12 - Rotary kiln, 13 - Burner, 141 - Hot air exhaust pipe, 142 - Bag filter, 143 - Main exhaust fan, 21 - First spiral feeder, 22 - Reduction reactor, 23 - Discharge chute, 24 - Second spiral feeder, 25 - Feeding chute, 26 - Reducing agent bin, 27 - Reducing agent spiral feeder, 28 - Temperature sensor, 31 - Sealed stirring tank, 32 - Slurry pump, 33 - Exhaust pipe, 41 - Water bath dust collector, 42 - Return air fan, 43 - Gas transmission pipeline, 221 - Driving device, 222 - Cylinder body, 223 - Internal spiral blade, 224 - Lifting plate, 225 - Central shaft, 226 - Sealing mechanism. Detailed Embodiments
[0017] The present invention will be described in detail below with reference to the embodiments.
[0018] A limonite coal-based oxidative-reduction roasting system of the present invention is characterized in that it includes an oxidative roasting system, a reduction roasting system, a cooling and pulping system, and a hot air circulation system connected in sequence. The oxidative roasting system includes a quantitative feeder 11, a rotary kiln 12, and a burner 13. The discharge port of the quantitative feeder 11 is connected to the feed port of the rotary kiln 12, and the burner 13 is arranged at the kiln head of the rotary kiln 12. The reduction roasting system comprises a first screw feeder 21, a reducing agent bin 26, a reducing agent screw feeder 27, a reduction reactor 22, a discharge chute 23, a second screw feeder 24 and a feeding chute 26, wherein the first screw feeder 21 is arranged at the bottom of the rotary kiln head, and the feed port of the first screw feeder 21 is connected to the discharge port of the rotary kiln 12, the reducing agent screw feeder 27 is arranged at the upper side of the first screw feeder 21, the feed port of the reducing agent screw feeder 27 is connected to the reducing agent bin 26, the discharge port of the first screw feeder 21 and the discharge port of the reducing agent screw feeder 27 are both connected to the feed port of the reduction reactor 22, one end of the second screw feeder 24 is connected to the discharge port of the reduction reactor 22 through the discharge chute 23, and the other end is connected to the feeding chute 25; The cooling pulping system comprises a sealed stirring tank 31, a slurry pump 32 and an exhaust pipe 33. A spray water system is provided in the sealed stirring tank 31. The feed chute 25 is connected to the feed port of the sealed stirring tank 31 and inserted into the sealed stirring tank 31. The slurry pump 32 is connected to the lower discharge port of the sealed stirring tank 31. The hot air circulation system includes a water bath dust collector 41, a return air fan 42 and an air supply pipeline 43. One end of the exhaust pipe 33 of the cooling pulping system passes through the top cover of the sealed stirring tank 31 and is connected to the sealed stirring tank 31, and the other end is connected to the air inlet of the water bath dust collector 41. One end of the return air fan 42 is connected to the air outlet of the water bath dust collector 41, and the other end is connected to the exhaust pipeline 43. The end of the exhaust pipeline 43 is connected to the kiln head of the rotary kiln 12 and is arranged at the upper end of the burner 13 of the oxidation roasting system to connect the systems into a closed circuit.
[0019] The present invention further provides a fume treatment system at the kiln tail of the rotary kiln 12 , and the fume treatment system includes a hot air fume exhaust duct 141 , a bag filter 142 and a main exhaust fan 143 .
[0020] The end of the exhaust pipe 43 of the present invention is arranged 100 mm above the burner 13 of the oxidation roasting system.
[0021] The reduction reactor 22 described in the present invention is an internal spiral reactor, which includes a driving device 221, a cylinder body 222, a stirring main shaft 225, spiral blades 223 arranged on the stirring main shaft 225, and sealing mechanisms 226 arranged at both ends of the stirring main shaft 225. Lifting plates 224 are arranged at intervals on the side surface of the spiral blades 223. A feed inlet for entering and an input port for passing the reducing agent are arranged at the top of the reduction reactor. A discharge chute 23 is arranged at the right end of the reduction reactor, and a temperature sensor 28 is also arranged on the chute pipe. The inner wall of the cylinder body 222 is provided with refractory bricks or castables. The lifting plates 224 arranged on the inner spiral blades 223 can lift the materials to the highest point of the spiral. The stirring main shaft 225 and the rotating surface of the cylinder body 222 adopt a sealing mechanism 226 to ensure the airtightness inside the cylinder body 222. The driving device 221 is a variable-frequency speed-regulating motor, which ensures that the materials stay in the reactor 4 for 50 minutes. The pitch of the inner spiral blades 223 is designed according to two factors: when the driving device 221 is at 30HZ, the materials can stay for 50 minutes, and the filling degree of the materials in the cylinder body 222 reaches 90%. The setting of the temperature sensor 28 is used to control the feeding temperature of the reducer.
[0022] For a certain limonite raw ore with an iron grade of 35 - 55%, it is crushed to a particle size of -3mm. The coal used is a certain raw coal from Shaanxi, with a calorific value of 6500 kcal, a volatile content of 28%, an ash content of 24%, and a fixed carbon content of 65%. The coal is prepared into 40% powder of -200 mesh by a pulverizer. The above-mentioned limonite coal-based oxidation-reduction roasting system is used for coal-based oxidation-reduction roasting of limonite. The specific steps are as follows: Step 1 Oxidation roasting operation The limonite is fed into the feed inlet of the rotary kiln 12 by a metering feeder 11, and the burner 13 sprays fire into the kiln body for heating. The limonite goes through three stages of drying, preheating, and calcination in the rotary kiln 12. The temperature of the materials in the oxidation section is controlled at 700°C ± 25 to achieve the preheating, oxidation, and roasting of the materials. The hot flue gas generated in the rotary kiln 12 is discharged to the flue gas treatment system through the hot air exhaust pipe 141, the bag filter 142, and the main exhaust fan 143. Step 2 Reduction roasting operation The limonite after oxidation and roasting is fed into the reduction reactor from the discharge port of the rotary kiln through the first spiral feeder. The reducing agents are oxygen enhancer, calcium hydroxide, and pulverized coal. The weight ratio of the three raw materials is: 7 parts of coal, 2.5 parts of oxygen enhancer, and 0.5 part of calcium hydroxide. They are mixed in proportion by the wet method. The reducing agents form a CO reduction atmosphere inside the reduction reactor. 10 kg of reducing agent is added to each ton of limonite in proportion.
[0023] The reduction reactor 22 adopts an internal spiral reactor. The rotation of the internal spiral ensures the full mixing of the reducing agent and the material. The driving device 221 of the reduction reactor uses a variable-frequency speed-regulating motor to ensure that the residence time of the material in the cylinder is 50 minutes. The specific designed residence time is determined according to laboratory tests. The lifting plate 224 on the spiral blade 223 lifts the material to the highest point of the spiral, which is conducive to the full reaction of the material with the reduction gas, enabling the material to be reduced to magnetite. The temperature of the material discharged from the reduction reactor 22 after roasting is 600 °C; Step 3: Cooling and pulping operation The reduced magnetite is fed into the sealed stirring tank 31 through the discharge chute 25. The spraying water system in the sealed stirring tank 31 directly quenches the material with water and stirs and mixes it into a pulp with a concentration of 40%, and then it is transported to the subsequent grinding and separation operation system through the slurry pump 32; Step 4: Hot air circulation operation After the excess flue gas in the reduction reactor 22 passes through the first water bath in the sealed stirring tank 31, it undergoes primary dust removal. Then, after the dust and water vapor in the flue gas are secondary purified by the water bath dust collector, it is transported to the kiln head of the rotary kiln by the return air fan for waste gas combustion. The dust-containing slurry in the water bath dust collector returns to the stirring tank to form a closed-loop cycle. In this way, the waste heat is fully utilized, and at the same time, it plays a good environmental protection role.
[0024] The present invention is also applicable to the coal-based oxidative-reductive roasting of hematite and siderite. Implementation effect
[0025] A certain limonite is directly fed into an 1800G wet drum magnetic separator without undergoing the oxidative-reductive roasting process and cannot be effectively separated.
[0026] Calculated at 6500 kcal, for the traditional single-stage rotary kiln reduction roasting system: 50 kg of coal is allocated per ton of limonite for reduction and fed into the rotary kiln through a metering feeder. The residence time of the material in the kiln is 50 minutes, and 30 kg of coal is used for combustion. The temperature of the high-temperature section is controlled at 800 °C. The discharged material is directly quenched with water, and the prepared pulp is also fed into an 1800G wet drum magnetic separator. For the single-stage rotary kiln of the present invention, no internal coal is required. 40 kg of coal is used for combustion per ton of limonite, and 10 kg of reducing agent is used and fed into the reduction reactor. The comparison of the implementation results with the present invention patent is shown in Table 1:
[0027] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and substitutions can be made, and these improvements and substitutions should also be regarded as the protection scope of the present invention.
Claims
1. A limonite coal-based oxidation-reduction roasting system, characterized in that: It includes the oxidation roasting system, reduction roasting system, cooling pulping system and hot air circulation system connected in sequence. The oxidation roasting system comprises a quantitative feeder, a rotary kiln and a burner, wherein the discharge port of the quantitative feeder is connected to the feed port of the rotary kiln, and the burner is arranged at the kiln head of the rotary kiln; The reduction roasting system comprises a first screw feeder, a reducing agent bin, a reducing agent screw feeder, a reduction reactor, a discharge chute, a second screw feeder and a feeding chute, wherein the first screw feeder is arranged at the bottom of the rotary kiln head, the feed inlet of the first screw feeder is connected to the discharge outlet of the rotary kiln, the reducing agent screw feeder is arranged at the upper side of the first screw feeder, the feed inlet of the reducing agent screw feeder is connected to the reducing agent bin, the discharge outlet of the first screw feeder and the discharge outlet of the reducing agent screw feeder are both connected to the feed inlet of the reduction reactor, one end of the second screw feeder is connected to the discharge outlet of the reduction reactor through the discharge chute, and the other end is connected to the feeding chute; The cooling pulping system comprises a sealed stirring tank, a slurry pump and a spraying system. The sealed stirring tank is provided with a spraying water system. The feed chute is connected to the feed port of the sealed stirring tank and inserted into the sealed stirring tank. The slurry pump is connected to the lower discharge port of the sealed stirring tank. The hot air circulation system includes a water bath dust collector, a return air fan and an air transmission pipeline. One end of the exhaust pipe of the cooling pulping system passes through the top cover of the sealed stirring tank and is connected to the sealed stirring tank, and the other end is connected to the air inlet of the water bath dust collector. One end of the return air fan is connected to the air outlet of the water bath dust collector, and the other end is connected to the exhaust pipeline. The end of the exhaust pipeline is connected to the kiln head of the rotary kiln and is arranged at the upper end of the burner of the oxidation roasting system to connect the systems into a closed circuit.
2. The limonite coal-based oxidation-reduction roasting system according to claim 1, characterized in that: A flue gas treatment system is also provided at the kiln tail of the rotary kiln. The flue gas treatment system includes a hot air exhaust pipe, a bag filter and a main exhaust fan.
3. The limonite coal-based oxidation-reduction roasting system according to claim 1, characterized in that: The end of the exhaust pipe is arranged 100 mm above the burner of the oxidation roasting system.
4. The limonite coal-based oxidation-reduction roasting system according to claim 1, characterized in that: The reduction reactor is an internal spiral reactor, including a driving device, a cylinder, a stirring main shaft, a spiral blade arranged on the outside of the stirring main shaft and a sealing mechanism. Lifting plates are arranged at intervals on the sides of the spiral blades. A feed inlet for entry and an input inlet for passing the reducing agent are arranged on the top of the reduction reactor. A discharge chute for discharging is arranged at the right end of the reduction reactor, and a temperature sensor is also arranged on the chute.
5. A method for oxidizing and reducing roasting of limonite coal, which is implemented by using the oxidizing and reducing roasting system of limonite coal according to claims 1-4, characterized in that: The following steps are involved: Step 1 Oxidation roasting operation The limonite is fed into the feed port of the rotary kiln by a quantitative feeder, and heated by spraying fire into the kiln body through a burner. The limonite is dried, preheated, and calcined in the rotary kiln, and the material is heated to 680℃-800℃ to achieve preheating, oxidation, and roasting of the material; the hot flue gas generated in the rotary kiln is discharged to the flue gas treatment system through the hot air exhaust pipe, bag dust collector, and main exhaust fan; Step 2: Reduction roasting After oxidation and roasting, the limonite is fed into the reduction reactor from the outlet of the rotary kiln through the first screw feeder. The reducing agent is an oxygenator, calcium hydroxide and coal powder, which are mixed in proportion by a wet method. The reducing agent forms a CO reducing atmosphere inside the reduction reactor. The reduction reactor adopts an inner spiral reactor. The rotation of the inner spiral ensures that the reducing agent and the material are fully mixed, and the residence time of the material in the cylinder is controlled to be 30-60 minutes. The designed residence time is determined according to laboratory tests. The lifting plate on the spiral blade lifts the material to the highest point of the spiral, which is conducive to the full reaction of the material and the reducing gas, and the oxide ore is reduced to magnetite. Step 3: Cooling and pulping The reduced magnetite is fed into the sealed stirring tank through the discharge chute. The spray water system in the sealed stirring tank directly hydrates the material and stirs and mixes it into a 40% concentration slurry, which is then transported to the back-end grinding and selection system through the slurry pump 32. Step 4: Hot air circulation operation The excess flue gas in the reduction reactor passes through a sealed stirring tank for a water bath and dust reduction, and then passes through a water bath dust collector to purify the dust and water vapor in the flue gas for a second time. The flue gas is then transported to the kiln head of the rotary kiln by the return air fan for exhaust gas combustion. The dust-containing slurry in the water bath dust collector returns to the stirring tank to form a closed loop.
6. The method for coal-based oxidation-reduction roasting of limonite according to claim 5, characterized in that: The limonite has an iron grade of 35-55%, a particle size of -3 mm, a coal powder of -200 mesh 40%, a calorific value of 6500 kcal, a volatile matter of 28%, an ash content of 24%, and a fixed carbon content of 65%.
7. The method for coal-based oxidation-reduction roasting of limonite according to claim 5, characterized in that: The reducing agent is composed of three raw materials: oxygenator, calcium hydroxide and coal powder, with the weight ratio being 7 parts of coal, 2.5 parts of oxygenator and 0.5 parts of calcium hydroxide.
8. The method for coal-based oxidation-reduction roasting of limonite according to claim 5, characterized in that: In the step 3, the temperature of the ore pulp in the cooling and pulping operation is controlled at ≤60°C.
9. The method for coal-based oxidation-reduction roasting of limonite according to claim 5, characterized in that: The oxygenator is any one or more combinations of calcium hypochlorite, sodium percarbonate, peramide, calcium peroxide, hydrogen peroxide or ammonium persulfate.