TWI632117B - A METHOD FOR PREPARING MAGNETIC MnFe2O4 FROM DRINKING-WATER TREATMENT SLUDGE - Google Patents

Abstract

The invention relates to a method for preparing iron-manganese oxide magnets from water purification sludge. In this method for preparing an iron-manganese oxide magnet, firstly, a water purification sludge is prepared, and the water purification sludge includes iron and manganese metals; then, the water purification sludge is impregnated with an acid washing solution to dissolve the water purification sludge Iron and manganese metal ions in iron; then, the iron-manganese-containing solution impregnated with the pickling solution is separated from the sludge and reduced with a reducing agent; then, the iron-manganese-containing solution is subjected to a high-temperature sintering reaction to form an iron-manganese oxide magnet Finished product.

Description

Method for preparing iron-manganese oxide magnet by using water purification sludge

The invention relates to a method for preparing an iron-manganese oxidized magnet, in particular to a method for preparing an iron-manganese oxidized magnet from water purification sludge containing iron-manganese metal.

According to the statistics of the Taiwan Water Supply Company in the Republic of China in 102 years, the annual domestic water consumption of each person in Taiwan was 94.6 tons. However, the water purification sludge is a waste that must be generated in the water purification process. It is estimated that the annual amount of water purification sludge produced in Taiwan exceeds 150,000 metric tons, the treatment cost of each metric ton of purified water sludge will vary from NT $ 300 to 1,000 depending on the sludge moisture content and the location of the water purification plant. The final disposal method of early water purification sludge was dewatering for incineration or landfill disposal. However, in recent years, because most landfill sites have become saturated and the cost of sludge treatment has increased year by year, a large amount of waste water purification sludge is buried. It is not a good disposal method. If such waste sludge can be effectively used, it will definitely save a lot of cleaning and transportation costs.

The types of sludge produced by the water purification program generally include pre-precipitated sludge, coagulated sludge, lime sludge, and iron and manganese sludge, of which iron and manganese sludge is produced by removing iron and manganese during the precipitation process. , The sludge solids are composed of iron oxide, manganese oxide and other iron and manganese compounds. In view of the fact that water purification sludge contains a large amount of iron and manganese elements, it has recycling value. Therefore, if the iron and manganese element recovery in such water purification sludge can be effectively utilized, further preparation of iron and manganese oxide materials with application potential will be possible. Achieve the purpose of reducing a large number of treatment costs, waste pollution reduction and resource reuse.

Iron oxide is the original source of ferrite magnets, and ferrite magnets are very important ceramic materials in the electronics and communications industries. At present, many ferrite magnets such as manganese-zinc, nickel-zinc, zinc-based, and lithium-based ferromagnets are prepared by the solid-state reaction method using α-Fe2O3 and other metals (such as MnO, ZnO, NiO, LiO, etc.). For the synthesis of ferrite magnets, hydrothermal synthesis, Sol-gel method, and high-temperature synthesis are commonly used. Among them, the hydrothermal synthesis method requires water or other substances as a solvent, and the reaction is complete. The wastewater containing the genus Osmanthus produced in the process may be harmful to the environment. When a highly volatile solvent is added or the activity is higher, In the case of strong gas, there is a possibility of explosion due to the high pressure in the reactor or the temperature of the reaction being too high. The sol-gel method has the disadvantages of high cost of bream production, long reaction time, harmful organic solvents used in the reaction, strict control of the environmental pH value during the reaction, and inability to produce larvae. As for the high-temperature synthesis method (also known as solid-phase sintering), although it has the advantages of low preparation cost, high repeatability, and high yield, the traditionally prepared ferrite powder has a large particle size and poor low-temperature co-firing characteristics. Restricted its industrial application.

For this reason, the present invention is mainly to propose a method for preparing iron-manganese oxide magnets from water purification sludge, which can dissolve iron-manganese metal ions in the water purification sludge, and at the same time, make the dissolved iron-manganese metal into a highly commercial product. The value and industrial application of ferromanganese oxidized magnets can reduce the heavy metal pollution of water purification sludge and reduce the cost of treating water purification sludge.

An embodiment of the method for preparing iron-manganese oxide magnets from water purification sludge according to the present invention includes: performing a step of preparing water purification sludge, the water purification sludge including iron and manganese metals; and performing an acid washing step to An acid pickling solution is used to soak the water purification sludge to dissolve iron and manganese metal ions in the water purification sludge, wherein the concentration of the acid washing solution is between 0.5-6M; a solid-liquid separation step is performed to remove the acid washing solution The impregnated iron-manganese metal ion solution is separated from the silicates in the purified water sludge; a reduction step is performed to use a reducing agent to make a portion of the ferric-manganese metal ion solution in the ferric-manganese metal ion solution (Fe ^{3 +} ) Into divalent iron ions (Fe ²⁺ ); finally, a calcination step is performed to subject the iron-manganese-containing metal ion solution to a high-temperature sintering reaction to form a finished iron-manganese oxide magnet.

In one embodiment, a grinding step is performed after the calcination step to grind the finished iron-manganese oxide magnet magnet to a desired particle size. After the grinding step, the iron manganese oxide magnet product is subjected to a washing step to wash the sludge (that is, to filter impurities) that does not form the iron manganese oxide magnet, and a drying step is performed after the washing step is completed.

In one embodiment, the pickling solution is nitric acid, the immersion temperature is controlled between 30-80 degrees Celsius, and the immersion time is controlled between 30-300 minutes.

Other objects, advantages and features of the present invention will be understood from the following detailed description of the preferred embodiments and with reference to the accompanying drawings.

FIG. 1 illustrates an oxide magnet preparation system 100 used in a method according to an embodiment of the present invention, and FIG. 2 illustrates steps of a method for preparing an iron-manganese oxide magnet according to the present invention. As shown in FIG. 1, the oxide magnet preparation system 100 includes a mixing device 110, a solid-liquid separation device 120, a reaction tank 130, a calcining device 140, a grinding device 150, and a drying device 160. As shown in FIG. 2, in this embodiment, the method for preparing iron-manganese oxide magnets using water purification sludge in the present invention includes: performing a water purification sludge preparation step 210, performing an acid washing step 220, and performing solid-liquid separation. Step 230, performing a reduction step 240, performing a calcination step 250, performing a grinding step 260, and performing a drying step 270.

In the step 210 of preparing water purification sludge, the water purification sludge includes iron and manganese metals and is stored in a sludge storage tank 170. In one embodiment, the real-world water sludge is crushed, and then sieved with a 45-mesh sieve (pore size 0.297mm). The clean water sludge with a particle size less than 0.297mm is taken and placed in an oven at 105 ° C. After 12 hours of drying, it is placed in the sludge storage tank 170 for backup.

In the pickling step 220, the pickling solution is used to soak the purified water sludge to dissolve the iron and manganese metal ions in the purified water sludge. In one embodiment, the water purification sludge is impregnated with nitric acid to dissolve the iron and manganese metal ions in the water purification sludge, wherein the nitric acid concentration is between 0.5-6M, the immersion time is between 30-300 minutes, and the immersion temperature Between 25-90 ° C. In an acid pickling test, dried real-field sludge and nitric acid of different concentrations (0.5, 1, 1.5, 2, 2.5, 3, 4, 5, 6M) were used in a mixing device 110 at a rotational speed of The stirring device 180 at 150 rpm stirs to soak the purified water sludge, the soaking temperature is 25 ° C., and the stirring is 120 minutes; as shown in FIG. 3, the nitric acid concentration used to dissolve the total iron and total manganese is preferably between 0.5-6M, And it can dissolve the maximum iron and manganese at 2M. In another pickling immersion test, the effect of leaching time on the leaching efficiency of iron and manganese was tested through different immersion times (30, 60, 90, 120, 150, 180, 210, 240, 270, and 300 minutes). The dried real-field sludge and nitric acid having a concentration of 2M are stirred and mixed in a mixing device 110 to impregnate the purified water sludge at a temperature of 25 ° C; the results are shown in FIG. 30-120 minutes is preferred, the immersion time is 60-90 minutes, and the most preferred is 60 minutes. The prolonged immersion time may cause the change of manganese type and adversely affect the dissolution of manganese. In another pickling immersion test, the effect of the immersion temperature on the leaching efficiency of iron and manganese ions was tested through different immersion temperatures (25, 30, 40, 50, 60, 70, 80, and 90 ° C). Real-field sludge and 2M nitric acid were stirred in the mixing device 110 for 60 minutes; as shown in Figure 5, the immersion temperature was controlled at 30-80 degrees, with 50-70 degrees being preferred, and 60-70 degrees being better. , 70 degrees is the best. When the immersion temperature is higher than 70 ° C, the reaction temperature may be too high, which causes the sludge to oxidize and cause the sludge dissolution rate to decrease rapidly.

In the solid-liquid separation step 230, the solid-liquid separation device 120 is used to separate the iron-manganese-containing metal ion solution in the pickling step 220 from the silicates in the purified water sludge. The solid-liquid separation device 120 used in this embodiment includes a filtering screen, which can filter out solid sludge to separate liquid and solid, but the invention is not limited thereto.

In the reduction step 240, the iron-manganese metal ion solution impregnated with the pickling solution and the urea reducing agent, for example, 0.5 to 2M (1.66M in this example) are stirred and dissolved in the reaction tank 130 to make iron-containing Some of the trivalent iron ions (Fe ³⁺ ) in the manganese metal ion solution become divalent iron ions (Fe ²⁺ ). In a feasible embodiment, the reducing agent is glucose.

In the calcination step 250, the iron-manganese metal ion solution impregnated by the pickling solution is subjected to a high-temperature sintering reaction to form a finished product having an iron-manganese oxide magnet. In a specific embodiment, the iron-manganese metal ion solution impregnated by the pickling solution is put into a high-temperature calcining device 140 to perform calcination at a high temperature of 500-600 ° C and a time of 1-4 hours. The iron-manganese oxidized magnet product can be obtained by performing high-temperature calcination at 600 ° C for 1-2 hours.

In the grinding step 260, the calcined product is ground to a desired particle size by the grinding device 150. Before the drying step 270 is performed, a washing step 280 may be performed to wash the sludge that does not form an iron-manganese oxide magnet. In one embodiment, the reverse osmosis water (RO water) is used to wash the sludge without forming the iron-manganese oxide magnet in a washing device 190. In the drying step 270, the finished product is dried by using the drying device 160 to prepare a ferromanganese oxide magnet finished product. In this embodiment, the iron manganese oxide magnet has a very fine granular appearance. It is black in color and magnetic.

According to a preferred embodiment of the method of the present invention, when the concentration of nitric acid is 2.0M, the highest total iron and total manganese can be simultaneously pickled out. And under the operating conditions of a reaction time of 60 minutes, a reaction temperature of 70 ° C, and a stirring speed of 150 rpm, the best dissolution efficiency of total iron and total manganese can be obtained from the purified water sludge. Furthermore, the qualitative analysis of the iron-manganese oxide magnet prepared by the present invention is performed by an analysis device such as an X-ray diffractometer (XRD), a scanning electron microscope (SEM), and a superconducting quantum interference vibration magnetometer (SQUID VSM). Then, it was confirmed that the finished product of the iron-manganese oxide magnet was paramagnetic MnFe2O4 magnetic nano particles. In a specific analysis, as shown in FIG. 6, using a superconducting quantum interference vibration magnetometer (SQUID VSM) to detect the magnetization of the ferromanganese oxide magnet (MnFe2O4) and the saturated magnetic water purification sludge prepared by the present invention, we can obtain The saturation magnetization of the saturated magnetic water purification sludge is 0.75 emu / g, and the saturation magnetization of the ferromanganese oxide magnet (MnFe2O4) prepared by the present invention is 23.20 emu / g. According to the results, the ferromanganese oxide magnet (MnFe2O4) prepared by the present invention ) Magnetic nano particles are paramagnetic.

In the foregoing description, the present invention has been described only with reference to specific embodiments, and various changes or modifications can be made according to the features of the present invention. Therefore, obvious replacements and modifications that can be made by those skilled in the art will still be included in the scope of patents claimed by the present invention.

100. Oxidation magnet preparation system 110. Mixing device

120. Solid-liquid separation device 130. Reaction tank

140 calcining device 150. grinding device

160. Drying device 170. Sludge storage tank

180. Mixing device 190. Washing device

210. Step for preparing water purification sludge 220. Step for pickling

230. solid-liquid separation step 240. reduction step

250. Calcination step 260. Grinding step

270. drying step 280. washing step

FIG. 1 is a schematic diagram of equipment of an oxide magnet preparation system according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing the steps of the method for preparing iron-manganese oxide magnets using water purification sludge according to the present invention.

FIG. 3 is a graph showing the relationship between the concentration of nitric acid and the dissolution of total iron and manganese in the pickling step.

FIG. 4 is a graph showing the relationship between the reaction time and the total iron and manganese dissolution content during the pickling step.

Fig. 5 is a graph showing the relationship between the effect of heating temperature on the dissolution of total iron and manganese in the pickling step.

FIG. 6 is a comparison diagram of magnetization curves of ferromanganese oxide magnets and water purification sludge prepared by the present invention.

Claims (9)

A method for preparing iron-manganese oxide magnets from water purification sludge, including: performing a step of preparing water purification sludge, the water purification sludge including iron and manganese metals; and performing a pickling step to impregnate the solution with a pickling solution Water purification sludge dissolves iron and manganese metal ions in the water purification sludge, wherein the concentration of the pickling solution is between 0.5-6M, the immersion temperature is controlled between 30-80 degrees Celsius, and the immersion time is controlled between 30-300 Between minutes; performing a solid-liquid separation step to separate the iron-manganese metal ion solution impregnated by the pickling solution from silicates in the purified water sludge; and performing a reduction step to use a reducing agent to make the solid Part of the trivalent iron ion (Fe ³⁺ ) in the iron-manganese metal ion solution after the liquid separation step is changed into divalent iron ion (Fe ²⁺ ); and a calcination step is performed to change the iron content after the reduction step The manganese metal ion solution undergoes a high-temperature sintering reaction to form a ferromanganese oxide magnet finished product. The method for preparing iron-manganese oxide magnets from purified water sludge as described in item 1 of the scope of the patent application, wherein a grinding step is performed after the calcination step to grind the finished iron-manganese oxide magnets to the required The particle size. The method for preparing iron-manganese oxide magnets from purified water sludge as described in item 2 of the scope of the patent application, wherein after the grinding step, the finished product of iron-manganese oxide magnets is subjected to a rinsing step to remove the pollution that does not form iron-manganese oxide magnets. Mud, and after the washing step is completed, a drying step is performed to dry the ground iron-manganese oxide magnet product. The method for preparing iron-manganese oxidized magnet from purified water sludge as described in item 1 of the scope of patent application, wherein the reducing agent in the reducing step is urea or glucose. The method for preparing iron-manganese oxidized magnets from purified water sludge as described in item 1 of the scope of the patent application, wherein in the pickling step, the purified water sludge containing iron-manganese metal and the pickling liquid are stirred and mixed in a mixing device To dissolve the iron-manganese metal ions in the purified water sludge into the pickling solution. The method for preparing iron-manganese oxide magnets from purified water sludge as described in item 5 of the scope of the patent application, wherein the pickling solution is nitric acid, and the immersion temperature is controlled between 50-70 degrees. The method for preparing iron-manganese oxide magnets from purified water sludge as described in item 5 of the scope of the patent application, wherein the pickling solution is nitric acid, and the immersion time is controlled between 30-120 minutes. The method for preparing iron-manganese oxide magnets from water purification sludge as described in item 1 of the scope of the patent application, wherein in the step of preparing water purification sludge, the water purification sludge is crushed, and then sieved with a sieve to obtain pellets. Sludge with a diameter of less than 0.297mm is dried in an oven. The method for preparing iron-manganese oxide magnets from purified water sludge as described in item 1 of the scope of the patent application, wherein in the calcination step, the iron-manganese metal ion solution impregnated by the pickling solution is put into a high-temperature calcining device The calcination is performed at a temperature of 500-600 ° C and a time of 1-4 hours.