Method for improving grade of phosphorite and removing impurities by using calcination-digestion method

Abstract

The invention discloses a method for improving the grade of phosphorite and removing impurities through a calcination-digestion method, and relates to the technical field of phosphorite beneficiation. The method comprises the following steps: phosphorite crushing: phosphorite raw materials are conveyed to a jaw crusher for coarse crushing, ores subjected to coarse crushing enter a cone crusher for intermediate crushing, ores subjected to intermediate crushing enter a ball mill for fine crushing, and meanwhile, an ultrasonic vibration device is additionally arranged in the ball mill. Impurity wrapping is avoided and the subsequent reaction efficiency is improved by precisely regulating and controlling the granularity during crushing and by means of ultrasound, impurities are strongly decomposed and volatilized through precise temperature control, stable temperature rise and microwave assistance during calcination, phosphate is activated and enriched, the concentration, the liquid-solid ratio and the like are optimized in the digestion link, a chelating agent is added, deep impurity removal is achieved, and phosphorus recovery is guaranteed. Through fine control, the impurities are greatly reduced, the yield is remarkably improved, the product quality is optimized, meanwhile, efficient utilization of resources and environmental protection are considered, and innovation and sustainable development of the phosphorite beneficiation technology are powerfully promoted.

Description

Technical Field

[0001] The invention relates to the technical field of phosphate ore dressing, and in particular to a method for improving the grade of phosphate ore and removing impurities by using a calcination-digestion method. Background Art

[0002] The phosphate ore beneficiation methods include gravity separation, flotation, chemical leaching, magnetic separation, bioleaching, gas-solid separation, and electron beam separation. Currently, flotation is the phosphate ore beneficiation process with the best separation effect and the widest application range in the world. It is also a relatively mature method. There has been much research on Zhijin phosphate ore, and certain achievements have been made. However, a large amount of phosphorus-containing slag will be produced, resulting in serious waste of resources and cannot meet production requirements.

[0003] Although the calcination-digestion beneficiation method has many advantages, such as increasing the phosphate leaching rate, reducing the magnesium and calcium content, improving the crystallization performance, and meeting environmental protection requirements, existing research has mostly focused on calcination parameters, with less research on digestion, and insufficient research on the mineral characteristics, structural changes, and element migration of phosphate ore during the calcination-digestion process.

[0004] To this end, we provide a method for improving the grade of phosphate ore and removing impurities by calcination-digestion method to solve the above problems. Summary of the invention

[0005] The object of the present invention is to provide a method for improving the grade of phosphate ore and removing impurities by using a calcination-digestion method. Through the combination of calcination and digestion, the problems of resource waste, environmental pollution, and unsatisfactory effects of improving the grade of phosphate ore and removing impurities in the phosphate ore dressing process in the prior art are solved.

[0006] In order to solve the above technical problems, the present invention is achieved through the following technical solutions:

[0007] The present invention is a method for improving the grade of phosphate ore and removing impurities by using a calcination-digestion method, comprising the following steps: Step A: Phosphate ore crushing: transporting the phosphate ore raw material to a jaw crusher for coarse crushing, the coarsely crushed ore then enters a cone crusher for medium crushing, and the medium crushed ore enters a ball mill for fine crushing. At the same time, an ultrasonic vibration device is added inside the ball mill, and the ultrasonic frequency is set at 20-30kHz, and the ultrasonic cavitation effect is used to further refine the phosphate ore particles; Step B: calcination treatment: comprising the following processes: B1: temperature control: determining the calcination temperature range between 800°C and 1000°C according to the specific composition and characteristics of the phosphate ore , use a programmable logic controller (PLC) to accurately control the heating system of the calcining furnace. In the initial stage of heating, slowly heat up to 500℃ at a rate of 5-10℃ / min to initially volatilize the moisture and some volatile impurities in the phosphate ore, and then heat up to the set calcining temperature at a rate of 10℃ / min to 20℃ / min; B2: Time setting: The calcining time is set in the range of 1.5 hours to 3 hours. When the temperature in the calcining furnace reaches the set temperature, start timing. During the calcining process, as time goes by, the relevant impurities in the phosphate ore gradually undergo chemical reactions and achieve the expected removal or conversion effect; B3: Rising Temperature rate control: Use a stable and appropriate heating rate, controlled at 10℃ / min to 20℃ / min, so that the phosphate rock is evenly heated during the calcination process; Step C: Digestion treatment: It includes the following processes; C1: Digestion liquid selection and concentration preparation: Dilute nitric acid is used as the digestion liquid, and concentrated nitric acid is added to deionized water through a metering pump according to a set ratio, and fully stirred and mixed in a stirring tank to prepare a dilute nitric acid solution with a concentration between 2mol / L and 5mol / L; C2: Liquid-solid ratio determination: The liquid-solid ratio during digestion is set in the range of 3:1 to 5:1, and then the optimal ratio that can fully dissolve and separate the phosphate mineral is determined, The cooled calcined product is quantitatively added to the digestion reactor through a screw feeder, and at the same time, the prepared dilute nitric acid solution is added to the reactor according to the set liquid-to-solid ratio through another metering pump; C3: Digestion time control: The digestion time is controlled at 2 to 4 hours. In the digestion reactor, an agitator is installed, and the agitator speed is controlled at 150-300 rpm to ensure that the phosphate rock and dilute nitric acid are fully in contact and chemically react; C4: Digestion temperature maintenance: The digestion temperature is maintained at 40°C to 60°C. During the digestion process, the reaction system is continuously stirred to ensure that the reaction is carried out evenly, and corresponding exhaust gas treatment devices are also equipped.

[0008] The present invention is further configured as follows: in the step A, steel balls are loaded into the ball mill as grinding media, and the rotation speed of the ball mill is controlled at 15-25 revolutions per minute to fully grind the phosphate ore raw material, and the grinding time is 30-60 minutes to ensure that the phosphate ore particle size can pass through a 200-mesh standard sieve.

[0009] The present invention is further configured such that, during the crushing process in step A, the particle size of the phosphate ore particles is monitored in real time by an online particle size monitor to accurately control the degree of crushing, and when it is monitored that the particle size of the phosphate ore particles meets the requirements, the crushed phosphate ore particles are transported to a storage bin by airflow for standby use.

[0010] The present invention is further configured such that, during the calcination process in B1, a thermocouple thermometer and a pressure sensor installed in the calcination furnace are used to monitor the temperature and pressure in the furnace in real time, and the temperature and pressure data are transmitted to a PLC, and the PLC automatically adjusts the heating power and ventilation volume according to a preset temperature and pressure range.

[0011] The present invention is further configured such that a microwave-assisted heating device is introduced into the calcining furnace in B1, which is started after the temperature is raised to 600°C, and the microwave frequency is 915MHz. Through the coupling effect of microwaves and phosphate rock, the thermal vibration of internal minerals is enhanced, and the decomposition and conversion of impurities are promoted.

[0012] The present invention is further configured such that in B2, the impurity content and the grade of the phosphate ore in the calcined product are analyzed by regular sampling to determine the optimal calcination time.

[0013] The present invention is further configured that, during the calcination process in B3, key parameters of temperature and pressure in the furnace are monitored in real time to ensure that the entire calcination process is in a stable and controllable state. After the calcination is completed, the calcined product is transported to a cooling bin via a cooling conveyor belt, and the calcined product is cooled to room temperature by air cooling or water cooling, and then transported to a digestion treatment process.

[0014] The present invention is further configured such that the stirring speed in C1 is controlled at 100-200 rpm and the stirring time is 10-20 minutes to ensure uniform dispersion of nitric acid. On this basis, a small amount of chelating agent is added to the dilute nitric acid solution, and the added amount is 0.5%-2% of the mass of nitric acid. The complexation of the chelating agent with metal ions is utilized to enhance the removal effect of calcium and magnesium impurity metal ions.

[0015] The present invention is further configured such that, during the digestion process in C3, the temperature in the reactor is monitored in real time by a temperature sensor, and the reaction temperature is adjusted by a jacketed heat exchanger or a coil heat exchanger to control the temperature at 40°C to 60°C.

[0016] The present invention is further configured such that after the digestion of C4 is completed, the reaction product is separated into solid and liquid by filtering equipment, and the obtained solid is a phosphate rock product with improved grade and reduced impurity content, and the liquid enters the wastewater treatment system for treatment and then recycled or discharged in compliance with the standards.

[0017] The present invention has the following beneficial effects:

[0018] The present invention precisely controls the particle size during crushing and uses ultrasound to avoid impurity wrapping and improve the efficiency of subsequent reactions. It also uses precise temperature control, steady temperature rise and microwave assistance during calcination to strongly decompose volatile impurities and activate and enrich phosphates. In the digestion step, it optimizes the concentration, liquid-solid ratio, etc. and adds a chelating agent to deeply remove impurities and ensure phosphorus recovery. Such fine control can greatly reduce impurities, significantly improve output rate, optimize product quality, and take into account both efficient resource utilization and environmental protection, which effectively promotes the innovation and sustainable development of phosphate ore dressing technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for describing the embodiments are briefly introduced below.

[0020] Figure 1 The present invention is a flow chart of a method for improving the grade of phosphate ore and removing impurities by using a calcination-digestion method. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present invention will be described below in conjunction with the drawings in the embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0022] Example 1

[0023] A method for improving the grade of phosphate ore and removing impurities by calcination-digestion method, comprising the following steps: Step A: Phosphate ore crushing: The phosphate ore raw material is transported to a jaw crusher for coarse crushing, and the coarsely crushed ore is then transported to a cone crusher for medium crushing, and the medium crushed ore is transported to a ball mill for fine crushing, and steel balls are loaded into the ball mill as grinding media, and the rotation speed of the ball mill is controlled at 15-25 rpm to fully grind the phosphate ore raw material, and the grinding time is 30-60 minutes to ensure that the phosphate ore particle size can pass through a 200-mesh standard sieve. During the crushing process, the particle size of the phosphate ore particles is monitored in real time by an online particle size monitor to accurately control the degree of crushing. When it is monitored that the particle size of the phosphate ore particles meets the requirements, the crushed phosphate ore particles are transported to a storage bin through an airflow for standby use, and at the same time, an ultrasonic vibration device is added inside the ball mill, and the ultrasonic frequency is set at 20-30kHz, and the phosphate ore particles are further refined by the ultrasonic cavitation effect; Step B: Calcination treatment: comprising the following processes: B1: Temperature Control: According to the specific composition and characteristics of the phosphate rock, the calcination temperature range is determined to be between 800℃ and 1000℃. The programmable logic controller (PLC) is used to accurately control the heating system of the calcination furnace. In the initial stage of heating, the temperature is slowly raised to 500℃ at a rate of 5-10℃ / min to initially volatilize the moisture and some volatile impurities in the phosphate rock, and then the temperature is raised to the set calcination temperature at a rate of 10℃ / min to 20℃ / min. During the calcination process, the temperature and pressure in the furnace are monitored in real time by the thermocouple thermometer and pressure sensor installed in the calcination furnace, and the temperature and pressure data are transmitted to the PLC. The PLC automatically adjusts the heating power and ventilation volume according to the preset temperature and pressure range. A microwave auxiliary heating device is introduced into the calcination furnace and started after the temperature is raised to 600℃. The microwave frequency is 915MHz. Through the coupling effect of microwave and phosphate rock, the thermal vibration of the internal minerals is enhanced and the decomposition and transformation of impurities are promoted; B2: Time setting: The calcination time is set at 1.In the range of 5 hours to 3 hours, when the temperature in the calcining furnace reaches the set temperature, the timing starts. During the calcining process, as time goes by, the relevant impurities in the phosphate ore gradually undergo chemical reactions and achieve the expected removal or conversion effect. The impurity content and phosphate ore grade in the calcined product are analyzed by regular sampling to determine the optimal calcination time; B3: Heating rate control: A stable and appropriate heating rate is used, controlled at 10℃ / min to 20℃ / min, so that the phosphate ore is evenly heated during the calcining process. During the calcining process, the key parameters of temperature and pressure in the furnace are monitored in real time to ensure that the entire calcining process is in a stable and controllable state. After the calcination is completed, the calcined product is passed through The supercooling conveyor belt is transported to the cooling bin, and the calcined product is cooled to room temperature by air cooling or water cooling, and then transported to the digestion treatment process; Step C: Digestion treatment: It includes the following processes; C1: Digestion liquid selection and concentration preparation: Dilute nitric acid is selected as the digestion liquid, and concentrated nitric acid is added to deionized water according to the set ratio through a metering pump, and fully stirred and mixed in a stirring tank. The stirring speed is controlled at 100-200 rpm and the stirring time is 10-20 minutes to ensure that the nitric acid is evenly dispersed. On this basis, a small amount of chelating agent is added to the dilute nitric acid solution, and the added amount is 0.5%-2% of the mass of nitric acid. The complexation of the chelating agent and the metal ions is used to enhance the To improve the removal effect of calcium and magnesium impurities and metal ions, a dilute nitric acid solution with a concentration between 2mol / L and 5mol / L is prepared; C2: Determination of liquid-solid ratio: The liquid-solid ratio during digestion is set in the range of 3:1 to 5:1, and then the optimal ratio that can fully dissolve and separate the phosphate mineral is determined, and the cooled calcined product is quantitatively added to the digestion reactor through a screw feeder, and at the same time, the prepared dilute nitric acid solution is added to the reactor according to the set liquid-solid ratio through another metering pump; C3: Digestion time control: The digestion time is controlled at 2 hours to 4 hours. In the digestion reactor, an agitator is installed, and the agitator speed is controlled at 150-300 rpm. The phosphate rock is fully contacted with the dilute nitric acid and a chemical reaction occurs. During the digestion process, the temperature in the reactor is monitored in real time by a temperature sensor, and the reaction temperature is adjusted by a jacketed heat exchanger or a coil heat exchanger to control the temperature at 40°C to 60°C; C4: Digestion temperature maintenance: The digestion temperature is maintained at 40°C to 60°C. During the digestion process, the reaction system is continuously stirred to ensure that the reaction proceeds evenly. At the same time, the corresponding tail gas treatment device is equipped. After the digestion is completed, the reaction product is separated into solid and liquid through a filtering device. The solid obtained is a phosphate rock product with improved grade and reduced impurity content. The liquid enters the wastewater treatment system for treatment and then recycled or discharged in compliance with the standards.

[0024] Example 2

[0025] Preparation of phosphate rock raw materials: Select raw materials from specific phosphate rock sources, the main component of which is phosphate minerals, and contains a certain amount of carbonates, organic matter and other impurities.

[0026] Phosphate ore crushing: The phosphate ore raw materials are transported to the jaw crusher for coarse crushing. The coarsely crushed ore enters the cone crusher for medium crushing, and the medium crushed ore enters the ball mill for fine crushing. In the ball mill, steel balls are loaded as grinding media, and the speed of the ball mill is controlled at 20 rpm. The grinding time is 45 minutes. At the same time, the ultrasonic vibration device inside the ball mill is turned on, and the ultrasonic frequency is set at 25kHz. The ultrasonic cavitation effect is used to further refine the phosphate ore particles. The particle size of the phosphate ore particles is monitored in real time through the online particle size monitor. When the phosphate ore particle size can pass the 200-mesh standard sieve, the crushed phosphate ore particles are transported to the storage bin through the airflow for standby use.

[0027] Calcination treatment:

[0028] Temperature control: A programmable logic controller (PLC) is used to precisely control the heating system of the calcining furnace. In the initial stage of heating, the temperature is slowly raised to 500°C at a rate of 8°C / minute to initially volatilize the moisture and some volatile impurities in the phosphate rock, and then the temperature is raised to 900°C at a rate of 15°C / minute. During the calcining process, the temperature and pressure in the furnace are monitored in real time using a thermocouple thermometer and a pressure sensor installed in the calcining furnace, and the temperature and pressure data are transmitted to the PLC. The PLC automatically adjusts the heating power and ventilation volume according to the preset temperature and pressure range, and starts the microwave-assisted heating device after the temperature is raised to 600°C. The microwave frequency is 915MHz. Through the coupling effect of microwaves and phosphate rock, the thermal vibration of the internal minerals is enhanced, and the decomposition and transformation of impurities are promoted.

[0029] Time setting: When the temperature in the calcining furnace reaches 900°C, the timing starts and the calcination time is set to 2.5 hours. During the calcination process, as time goes by, the relevant impurities in the phosphate ore gradually undergo chemical reactions and achieve the expected removal or conversion effect. By regularly sampling and analyzing the impurity content and phosphate ore grade in the calcined product, it is determined that the calcination time is more appropriate.

[0030] Heating rate control: A stable heating rate of 15°C / minute is used to ensure that the phosphate rock is heated evenly during the calcination process. The temperature, pressure and other key parameters in the furnace are monitored in real time to ensure that the entire calcination process is in a stable and controllable state. After calcination is completed, the calcined product is transported to the cooling bin via a cooling conveyor belt, and the calcined product is cooled to room temperature by air cooling, and then transported to the digestion treatment process.

[0031] Digestion Processing:

[0032] Selection of digestion liquid and concentration adjustment: dilute nitric acid is used as the digestion liquid. Concentrated nitric acid is added into deionized water through a metering pump according to a set ratio, and the mixture is fully stirred and mixed in a stirring tank. The stirring speed is controlled at 150 rpm and the stirring time is 15 minutes. A dilute nitric acid solution with a concentration of 3.5 mol / L is prepared. A small amount of chelating agent ethylenediaminetetraacetic acid (EDTA) is added to the dilute nitric acid solution. The added amount is 1.2% of the mass of nitric acid. The complexation of the chelating agent with metal ions is utilized to enhance the removal effect of calcium and magnesium impurities and metal ions.

[0033] Determination of liquid-solid ratio: The liquid-solid ratio during digestion is set at 4:1. The cooled calcined product is quantitatively added to the digestion reactor through a screw feeder. At the same time, the prepared dilute nitric acid solution is added to the reactor according to the set liquid-solid ratio through another metering pump.

[0034] Digestion time control: The digestion time is controlled at 3 hours. A stirrer is installed in the digestion reactor, and the stirrer speed is controlled at 200 rpm to allow the phosphate rock to fully contact with dilute nitric acid and undergo a chemical reaction. During the digestion process, the temperature in the reactor is monitored in real time by a temperature sensor, and the reaction temperature is adjusted by a jacketed heat exchanger to control the temperature at 50°C.

[0035] Digestion temperature maintenance: The digestion temperature is maintained at 50°C. During the digestion process, the reaction system is continuously stirred to ensure that the reaction proceeds evenly. At the same time, the corresponding tail gas treatment device is equipped. After the digestion is completed, the reaction product is separated into solid and liquid through a filtration device. The solid obtained is a phosphate ore product with improved grade and reduced impurity content. The liquid enters the wastewater treatment system for treatment and then recycled or discharged in compliance with the standards. According to the test, the content of phosphorus pentoxide in the treated phosphate ore product is 25% higher than that of the original ore, and the content of major impurities such as calcium and magnesium is reduced by 40%.

[0036] Example 3

[0037] Preparation of phosphate rock raw materials: Select another phosphate rock source raw material, whose impurity composition is slightly different from that of Example 1, and the carbonate content is slightly higher.

[0038] Phosphate ore crushing: The phosphate ore raw materials are transported to the jaw crusher for coarse crushing, and the coarsely crushed ore is then sent to the cone crusher for medium crushing, and the medium crushed ore is sent to the ball mill for fine crushing. In the ball mill, steel balls are loaded as grinding media, and the speed of the ball mill is controlled at 18 rpm, and the grinding time is 50 minutes. At the same time, the ultrasonic vibration device inside the ball mill is turned on, and the ultrasonic frequency is set at 22kHz. The ultrasonic cavitation effect is used to further refine the phosphate ore particles. The particle size of the phosphate ore particles is monitored in real time through the online particle size monitor. When the phosphate ore particle size can pass the 200-mesh standard sieve, the crushed phosphate ore particles are transported to the storage bin through the airflow for standby use.

[0039] Calcination treatment:

[0040] Temperature control: A programmable logic controller (PLC) is used to precisely control the heating system of the calcining furnace. In the initial stage of heating, the temperature is slowly raised to 500°C at a rate of 6°C / minute to initially volatilize the moisture and some volatile impurities in the phosphate rock, and then the temperature is raised to 850°C at a rate of 12°C / minute. During the calcining process, the temperature and pressure in the furnace are monitored in real time using a thermocouple thermometer and a pressure sensor installed in the calcining furnace, and the temperature and pressure data are transmitted to the PLC. The PLC automatically adjusts the heating power and ventilation volume according to the preset temperature and pressure range, and starts the microwave-assisted heating device after the temperature is raised to 600°C. The microwave frequency is 915MHz. Through the coupling effect of microwaves and phosphate rock, the thermal vibration of the internal minerals is enhanced, and the decomposition and transformation of impurities are promoted.

[0041] Time setting: When the temperature in the calcining furnace reaches 850℃, start timing and set the calcination time to 2 hours. During the calcination process, as time goes by, the relevant impurities in the phosphate ore gradually undergo chemical reactions and achieve the expected removal or conversion effect. By regularly sampling and analyzing the impurity content and phosphate ore grade in the calcined product, it is determined that the calcination time is more appropriate.

[0042] Heating rate control: A stable heating rate of 12°C / minute is used to ensure that the phosphate rock is heated evenly during the calcination process. The temperature, pressure and other key parameters in the furnace are monitored in real time to ensure that the entire calcination process is in a stable and controllable state. After calcination is completed, the calcined product is transported to the cooling bin via a cooling conveyor belt, cooled to room temperature by water cooling, and then transported to the digestion treatment process.

[0043] Digestion Processing:

[0044] Selection of digestion liquid and concentration adjustment: dilute nitric acid is used as the digestion liquid. Concentrated nitric acid is added to deionized water through a metering pump according to a set ratio, and fully stirred and mixed in a stirring tank. The stirring speed is controlled at 120 rpm and the stirring time is 18 minutes. A dilute nitric acid solution with a concentration of 3 mol / L is prepared, and a small amount of chelating agent ethylenediaminetetraacetic acid (EDTA) is added to the dilute nitric acid solution. The added amount is 1% of the mass of nitric acid. The complexation of the chelating agent with metal ions is used to enhance the removal effect of calcium and magnesium impurities and metal ions.

[0045] Determination of liquid-solid ratio: The liquid-solid ratio during digestion is set at 3.5:1. The cooled calcined product is quantitatively added to the digestion reactor through a screw feeder. At the same time, the prepared dilute nitric acid solution is added to the reactor according to the set liquid-solid ratio through another metering pump.

[0046] Digestion time control: The digestion time is controlled at 3.5 hours. An agitator is installed in the digestion reactor, and the agitator speed is controlled at 250 rpm to allow the phosphate rock to fully contact with dilute nitric acid and undergo a chemical reaction. During the digestion process, the temperature in the reactor is monitored in real time by a temperature sensor, and the reaction temperature is adjusted by a coil heat exchanger to control the temperature at 45°C.

[0047] Digestion temperature maintenance: The digestion temperature is maintained at 45°C. During the digestion process, the reaction system is continuously stirred to ensure that the reaction proceeds evenly. At the same time, the corresponding tail gas treatment device is equipped. After the digestion is completed, the reaction product is separated into solid and liquid through a filtration device. The solid obtained is a phosphate ore product with improved grade and reduced impurity content. The liquid enters the wastewater treatment system for treatment and then recycled or discharged in compliance with the standards. According to the test, the content of phosphorus pentoxide in the treated phosphate ore product is 22% higher than that of the original ore, and the content of major impurities such as calcium and magnesium is reduced by 35%.

[0048] Example 4

[0049] Preparation of phosphate rock raw materials: Obtain a low-grade phosphate rock raw material with a relatively low phosphate content and a high proportion of carbonate impurities and a small amount of silicate impurities, etc.

[0050] Phosphate ore crushing: The phosphate ore raw materials are transported to the jaw crusher for coarse crushing. The coarsely crushed ore then enters the cone crusher for medium crushing, and the medium crushed product enters the ball mill for fine crushing. The ball mill is loaded with steel balls of specific specifications as grinding media, and the speed of the ball mill is controlled to be 16 rpm. The grinding time is 60 minutes. The ultrasonic vibration device inside the ball mill is running, and the ultrasonic frequency is set to 28kHz. The phosphate ore particles are refined by the ultrasonic cavitation effect, and the particle size is monitored in real time by the online particle size monitor. When the phosphate ore particles can pass through the 200-mesh standard sieve, the crushed phosphate ore particles are sent to the storage bin by airflow for standby.

[0051] Calcination treatment:

[0052] Temperature control: A programmable logic controller (PLC) is used to precisely control the heating system of the calcining furnace. The temperature is initially raised to 500°C at a rate of 7°C / minute to initially volatilize the moisture and some volatile impurities in the phosphate rock, and then the temperature is raised to 950°C at a rate of 18°C / minute. During the calcination period, the temperature and pressure in the furnace are monitored in real time using a thermocouple thermometer and a pressure sensor installed in the calcining furnace, and the data is transmitted to the PLC. The PLC automatically adjusts the heating power and ventilation volume according to the preset temperature and pressure range, and starts the microwave-assisted heating device when the temperature rises to 600°C. The microwave frequency is 915MHz, which enhances the internal mineral thermal vibration and promotes the decomposition and conversion of impurities.

[0053] Time setting: start timing when reaching 950℃, and set the calcination time to 1.8 hours. During the calcination process, the impurities in the phosphate rock undergo chemical reactions over time and achieve the expected removal or conversion effect. The optimal calcination time is determined by regularly sampling and analyzing the impurity content and phosphate rock grade of the calcined product.

[0054] Heating rate control: The phosphate rock is heated evenly at a stable heating rate of 18°C / minute, and key parameters in the furnace are monitored in real time to ensure that the calcination process is stable and controllable. After calcination is completed, the calcined product is sent to the cooling bin via a cooling conveyor belt, cooled to room temperature by air cooling, and then transported to the digestion treatment process.

[0055] Digestion Processing:

[0056] Digestive fluid selection and concentration preparation: dilute nitric acid is used as the digestive fluid, and concentrated nitric acid is added to deionized water in proportion through a metering pump. The mixture is fully stirred and mixed in a stirring tank at a stirring speed of 180 rpm for 12 minutes to prepare a dilute nitric acid solution with a concentration of 4 mol / L. At the same time, chelating agent ethylenediaminetetraacetic acid (EDTA) is added thereto in an amount of 0.8% of the mass of nitric acid. The removal efficiency of impurity metal ions such as calcium and magnesium is enhanced by the complexation of the chelating agent with metal ions.

[0057] Determination of liquid-solid ratio: Set the liquid-solid ratio during digestion to 4.5:1, add the cooled calcined product into the digestion reactor quantitatively via a screw feeder, and use another metering pump to add the prepared dilute nitric acid solution into the reactor according to the set liquid-solid ratio.

[0058] Digestion time control: The digestion time is controlled at 2.5 hours. In the digestion reactor, the agitator runs at a speed of 160 rpm to promote sufficient contact and reaction between the phosphate rock and dilute nitric acid. During the digestion process, the temperature in the reactor is monitored in real time by a temperature sensor, and the temperature is adjusted to 55°C using a jacketed heat exchanger.

[0059] Digestion temperature maintenance: The digestion temperature is maintained at 55°C, and the reaction system is continuously stirred to ensure uniform reaction. At the same time, an exhaust gas treatment device is equipped. After the digestion is completed, a filtration device is used to separate the solid and liquid. The solid obtained is a phosphate product with improved grade and reduced impurity content. The liquid enters the wastewater treatment system for treatment and then is recycled or discharged in compliance with the standards. According to the test, the phosphorus pentoxide content in the treated phosphate product is 28% higher than that of the original ore, and the content of major impurities such as calcium and magnesium is reduced by 45%.

[0060] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that technicians in the relevant technical field can better understand and utilize the present invention.

Claims

1. A method for improving the grade of phosphate ore and removing impurities by calcination-digestion method, characterized in that: The following steps are involved: Step A: Phosphate ore crushing: The phosphate ore raw material is transported to a jaw crusher for coarse crushing, and the coarsely crushed ore is then sent to a cone crusher for secondary crushing, and the secondary crushed ore is sent to a ball mill for fine crushing. At the same time, an ultrasonic vibration device is added inside the ball mill, and the ultrasonic frequency is set at 20-30kHz to further refine the phosphate ore particles by using the ultrasonic cavitation effect; Step B: Calcination treatment: including the following process: B1: Temperature control: According to the specific composition and characteristics of the phosphate rock, the calcination temperature range is determined to be between 800℃ and 1000℃. The heating system of the calcination furnace is accurately controlled by a programmable logic controller (PLC). In the initial stage of heating, the temperature is slowly raised to 500℃ at a rate of 5-10℃ / min to initially volatilize the moisture and some volatile impurities in the phosphate rock, and then the temperature is raised to the set calcination temperature at a rate of 10℃ / min to 20℃ / min; B2: Time setting: The calcination time is set within the range of 1.5 hours to 3 hours. When the temperature in the calcination furnace reaches the set temperature, the timing starts. During the calcination process, as time goes by, the relevant impurities in the phosphate ore gradually undergo chemical reactions and achieve the expected removal or conversion effect; B3: Heating rate control: Use a stable and appropriate heating rate, controlled at 10℃ / min to 20℃ / min, so that the phosphate rock is heated evenly during the calcination process; Step C: digestion treatment: including the following processes; C1: Digestive solution selection and concentration preparation: Dilute nitric acid is used as the digestive solution. Concentrated nitric acid is added to deionized water through a metering pump according to a set ratio, and fully stirred and mixed in a stirring tank to prepare a dilute nitric acid solution with a concentration between 2 mol / L and 5 mol / L; C2: Determination of liquid-solid ratio: The liquid-solid ratio during digestion is set in the range of 3:1 to 5:1, and then the optimal ratio that can fully dissolve and separate the phosphate minerals is determined. The cooled calcined product is quantitatively added to the digestion reactor through a screw feeder, and at the same time, the prepared dilute nitric acid solution is added to the reactor according to the set liquid-solid ratio through another metering pump; C3: Digestion time control: The digestion time is controlled between 2 hours and 4 hours. A stirrer is installed in the digestion reactor, and the stirrer speed is controlled at 150-300 rpm to allow the phosphate rock to fully contact with the dilute nitric acid and undergo a chemical reaction; C4: Digestion temperature maintenance: The digestion temperature is maintained at 40℃ to 60℃. During the digestion process, the reaction system is continuously stirred to ensure uniform reaction. At the same time, corresponding tail gas treatment equipment is equipped.

2. The method for improving the grade of phosphate ore and removing impurities by calcination-digestion method according to claim 1, characterized in that: In the step A, steel balls are placed in a ball mill as grinding media, and the rotation speed of the ball mill is controlled at 15-25 rpm to fully grind the phosphate rock raw material for 30-60 minutes to ensure that the phosphate rock particle size can pass through a 200-mesh standard sieve.

3. The method for improving the grade of phosphate ore and removing impurities by calcination-digestion method according to claim 1, characterized in that: In the crushing process of step A, the particle size of the phosphate ore particles is monitored in real time by an online particle size monitor to accurately control the degree of crushing. When it is monitored that the particle size of the phosphate ore particles meets the requirements, the crushed phosphate ore particles are transported to the storage bin through airflow for standby use.

4. The method for improving the grade of phosphate ore and removing impurities by calcination-digestion method according to claim 1, characterized in that: In B1, during the calcination process, the temperature and pressure in the furnace are monitored in real time using a thermocouple thermometer and a pressure sensor installed in the calcination furnace, and the temperature and pressure data are transmitted to the PLC, which automatically adjusts the heating power and ventilation volume according to the preset temperature and pressure range.

5. The method for improving the grade of phosphate ore and removing impurities by calcination-digestion method according to claim 1, characterized in that: In B1, a microwave-assisted heating device is introduced into the calcining furnace and started after the temperature is raised to 600° C. The microwave frequency is 915 MHz. Through the coupling effect of microwaves and phosphate rock, the thermal vibration of internal minerals is enhanced, and the decomposition and conversion of impurities are promoted.

6. The method for improving the grade of phosphate ore and removing impurities by calcination-digestion method according to claim 1, characterized in that: In B2, the impurity content and phosphate grade in the calcined product are analyzed by regular sampling to determine the optimal calcination time.

7. The method for improving the grade of phosphate ore and removing impurities by calcination-digestion method according to claim 1, characterized in that: In B3, during the calcination process, key parameters of temperature and pressure in the furnace are monitored in real time to ensure that the entire calcination process is in a stable and controllable state. After the calcination is completed, the calcined product is transported to the cooling bin through a cooling conveyor belt, and the calcined product is cooled to room temperature by air cooling or water cooling, and then transported to the digestion treatment process.

8. The method for improving the grade of phosphate ore and removing impurities by calcination-digestion method according to claim 1, characterized in that: The stirring speed in C1 is controlled at 100-200 rpm, and the stirring time is 10-20 minutes to ensure uniform dispersion of nitric acid. On this basis, a small amount of chelating agent is added to the dilute nitric acid solution, and the added amount is 0.5%-2% of the mass of nitric acid. The complexation of the chelating agent with metal ions is utilized to enhance the removal effect of calcium and magnesium impurity metal ions.

9. The method for improving the grade of phosphate ore and removing impurities by calcination-digestion method according to claim 1, characterized in that: In the digestion process of C3, the temperature in the reactor is monitored in real time by a temperature sensor, and the reaction temperature is adjusted by a jacketed heat exchanger or a coil heat exchanger to control the temperature at 40°C to 60°C.

10. The method for improving the grade of phosphate ore and removing impurities by calcination-digestion method according to claim 1, characterized in that: After the digestion of C4 is completed, the reaction product is separated into solid and liquid by filtering equipment. The obtained solid is a phosphate rock product with improved grade and reduced impurity content. The liquid enters the wastewater treatment system for treatment and then is recycled or discharged in compliance with the standards.

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