TWI443069B - Process for the preparation of six-valent iron - Google Patents

Description

Preparation method of hexavalent iron

The invention relates to a preparation method of hexavalent iron, in particular to a method for preparing hexavalent iron by using iron-containing sludge.

Along with the development of printed circuit board manufacturing, metal surface treatment industry and electroplating industry in Taiwan, a large amount of heavy metal waste liquid has also been produced. If heavy metal waste liquid and wastewater are not properly treated and discharged, it will cause extremely serious damage to the ecological environment. Therefore, the recycling and treatment of heavy metal-containing wastes and wastewater has been receiving considerable attention from the competent authorities and environmental groups.

Coagulation is a method commonly used in the treatment of heavy metal wastewater. At present, there are many kinds of coagulants, which can be divided into aluminum salt and iron salt. The main common inorganic coagulants are: aluminum sulfate, polyaluminum chloride, ferric chloride, ferrous sulfate, etc., generally using a coagulant to aluminum salt. The prevalence of coagulants as iron salts is mainly due to the fact that the aluminum salt coagulant does not cause drastic changes in the pH of the treated water and does not increase the color of the water. However, the use of coagulation to treat heavy metal wastewater produces large amounts of harmful sludge, causing serious sludge disposal problems. Therefore, it has been proposed to treat heavy metal wastewater with hexavalent iron.

Hexavalent iron is a water treatment agent with oxidation function and coagulation function, which can effectively remove suspended solids, heavy metals, and many water pollutants in water. The final product after the hexavalent iron reaction does not adversely affect the environment, so it is called a green oxidant. Hexavalent iron can be hydrolyzed into a highly charged product and Fe(OH) ₃ , which has good coagulation and adsorption, and heavy metals in water, such as Mn ₂ ⁺ , Cu ₂ ⁺ , Pb ₂ ⁺ , Cd ₂ ⁺ , Cr ₃ ⁺ and Hg ₂ ^+, there are good removal effect of the same concentration of heavy metals may be completely oxidized.

Since hexavalent iron has a strong ability to remove heavy metal ions in water, a low-cost preparation method of hexavalent iron is highly desirable.

One aspect of the present invention is to provide a method for preparing hexavalent iron to prepare hexavalent iron using iron-containing sludge.

According to an embodiment of the present invention, in the preparation method of the hexavalent iron, the moisture content of the iron-containing sludge is first adjusted according to a preset value. Next, the iron-containing sludge is subjected to an acid treatment step to uniformly mix the pickling liquid with the iron-containing sludge to dissolve the iron in the iron-containing sludge into the pickling liquid. Then, a solid-liquid separation step is performed to separate the pickling liquid from the iron-containing sludge. Next, a wet oxidation step is performed to oxidize iron ions in the acid wash solution with a oxidizing agent in a strong alkali environment to produce hexavalent iron ions. Then, a precipitation step is performed to form a ferrate salt with hexavalent iron ions using a salt.

Please refer to FIG. 1 and FIG. 2 simultaneously. FIG. 1 is a schematic diagram showing the apparatus of the hexavalent iron preparation system 100 according to an embodiment of the present invention, and FIG. 2 is a diagram showing the hexavalent value of the hexavalent iron preparation system 100. Schematic diagram of the process of the iron preparation method 200. The hexavalent iron preparation method 200 of the present embodiment can extract the iron component in the iron-containing sludge and prepare the hexavalent iron, so that not only the hexavalent iron having high utilization value can be obtained, but also the heavy metal of the sludge can be reduced at the same time. content.

The hexavalent iron preparation system 100 of the present embodiment includes an oscillating device 110, a solid-liquid separation device 120, a reaction tank 130, a stirring device 140, and a drying device 150. The hexavalent iron preparation system 100 and the hexavalent iron preparation method 200 will be described in detail below. Operating mechanism.

In the hexavalent iron preparation method 200 of the present embodiment, the moisture content adjustment step 210 is first performed to adjust the moisture content of the iron-containing sludge according to a predetermined value. In the present embodiment, the moisture content of the iron-containing sludge is adjusted to 10 to 20%. Then, a pickling step 220 is performed. In the pickling step 220, the sludge to be treated taken out from the sludge recovery tank 160 is placed in the oscillating device 110 together with the pickling liquid to be pickled to dissolve the iron in the sludge into the pickling liquid. In the present embodiment, pickling is carried out in an oscillating manner, and in the pickling liquid, nitric acid is used, but the embodiment of the present invention is not limited thereto.

Next, a solid-liquid separation step 230 is performed. In the solid-liquid separation step 230, the solid-liquid separation device 120 separates the acid-containing washing liquid containing iron from the mixture of the sludge and the pickling liquid in the step 220. The solid-liquid separation device used in the present embodiment includes a filter screen which can filter solid sludge to separate the liquid and the solid, but the solid-liquid separation device of the embodiment of the present invention is not limited thereto.

Then, a wet oxidation step 240 is performed. In the wet oxidation step 240, an acid-containing pickling solution, an oxidizing agent, an alkali agent, and a salt are added to the reaction tank 130, and uniformly mixed with the stirring device 140 to produce ferrate.

The oxidizing agent, the alkali agent and the salt of the present embodiment are selected from sodium hypochlorite, sodium hydroxide and potassium hydroxide, respectively. In the wet oxidation step 240, sodium hypochlorite is first placed in the reaction tank 130 together with the acid washing liquid to oxidize the iron in the acid washing liquid by using hypochlorite to change the ferric iron in the acid washing liquid into hexavalent iron. . Next, sodium hydroxide is added to the reaction tank 130 to provide an alkaline reaction environment to promote the oxidation of hypochlorite. Although sodium ferrate having hexavalent iron is obtained after the addition of sodium hydroxide, since sodium ferrate is an unstable compound, after the wet oxidation step 240, a precipitation step 250 is further performed to utilize a salt. It forms a ferrate with hexavalent iron ions and precipitates. In this embodiment, potassium hydroxide is added to the reaction tank 130 to precipitate a relatively stable potassium ferrate.

Then, a drying step 260 is performed to dry the moisture on the potassium ferrate using the drying device 150. In the present embodiment, the drying device 150 uses hot air to dry the moisture on the potassium ferrate, but the embodiment of the present invention is not limited thereto.

It can be seen from the above examples that the hexavalent iron preparation method 200 of the embodiment of the present invention uses waste iron-containing sludge as a raw material, and therefore the preparation cost of the hexavalent iron of the embodiment of the present invention is relatively low.

In addition, it is worth mentioning that in other embodiments of the invention, the hexavalent iron preparation may further comprise a temperature control step and an acid recovery step. In the wet oxidation step 240, when sodium hydroxide is added to the reaction tank 130, high heat energy is released and the temperature in the reaction tank 130 is greatly increased, which may adversely affect the subsequent chemical reaction. Therefore, when the wet oxidation step 240 is performed, the temperature control step is simultaneously performed to maintain the temperature of the reaction tank 130 between 25 and 30 degrees Celsius, so that adverse effects of high temperature can be avoided. In the acid recovery step, the ferric acid-containing washing liquid obtained from the solid-liquid separation step 230 is divided into two parts according to a predetermined recovery rate, one of which is used as a raw material for the formation of hexavalent iron, and the other is Partially recoverable as an acid wash in the pickling step, which reduces the consumption of pickling solution.

Although the invention has been disclosed above in several embodiments, it is not intended to The invention is defined by the general knowledge of the present invention, and various modifications and refinements can be made without departing from the spirit and scope of the invention. The scope is defined.

100‧‧‧ hexavalent iron preparation system

110‧‧‧ oscillating device

120‧‧‧Liquid separation device

130‧‧‧Reaction tank

140‧‧‧Agitator

150‧‧‧Drying device

160‧‧‧Sludge recovery tank

200‧‧‧ hexavalent iron preparation method

210‧‧‧Water content adjustment steps

220‧‧‧ pickling step

230‧‧‧ Solid-liquid separation steps

240‧‧‧ Wet oxidation step

250‧‧‧Precipitation step

260‧‧‧ drying step

The above and other objects, features and advantages of the present invention will become more <RTIgt; A schematic diagram of an apparatus for a hexavalent iron preparation system according to an embodiment of the invention.

2 is a schematic flow chart showing a method for preparing hexavalent iron according to an embodiment of the present invention.

200. . . Hexavalent iron preparation method

210. . . Moisture rate adjustment step

220. . . Pickling step

230. . . Solid-liquid separation step

240. . . Wet oxidation step

250. . . Precipitation step

260. . . Drying step

Claims (7)

A method for preparing hexavalent iron, comprising: performing a water content adjusting step to adjust a water content of an iron-containing sludge; performing an acid washing step to uniformly mix an acid washing liquid with the iron-containing sludge, thereby Dissolving iron in the iron-containing sludge into the pickling liquid; performing a solid-liquid separation step to separate the pickling liquid from the iron-containing sludge; performing a wet oxidation step to utilize an oxidizing agent Oxidizing iron ions in the pickling solution in a strong alkali environment to produce a hexavalent iron ion; and performing a precipitation step to add a salt to the pickling liquid to form a hexavalent iron ion Ferrate. The method for preparing hexavalent iron according to claim 1, further comprising a temperature control step for controlling the temperature of the pickling liquid between 25 and 30 degrees Celsius when the wet oxidation step is performed. . The method for preparing hexavalent iron according to claim 1, further comprising a drying step of drying the ferrate. The method for preparing hexavalent iron according to claim 1, wherein the pickling liquid is nitric acid. A method for preparing hexavalent iron according to claim 1, wherein The oxidizing agent is sodium hypochlorite. The method for preparing hexavalent iron according to claim 1, wherein the strong alkali environment is formed by sodium hydroxide. The method for preparing hexavalent iron according to claim 1, wherein the salt is potassium hydroxide.