CN108046307A - A kind of waste water extraction zinc of iron content containing zinc and the method for preparing zinc oxide - Google Patents

Abstract

The invention discloses a method for extracting zinc from waste water containing iron and zinc and preparing zinc oxide, which belongs to the field of waste resource utilization. The method is as follows: add liquid caustic soda to the sludge containing iron and zinc, stir evenly, adjust the pH value of the wastewater containing iron and zinc at 15°C to 35°C to 4-6.5, and at the same time introduce oxidizing gas to carry out low-temperature Oxidation, the oxidation time is 4‑8h. After ferrous oxide is completely oxidized, filter to obtain a solution, add alkaline substances at 15°C to 35°C to adjust the pH to 9-12, obtain white precipitate, filter, and dry at 130°C to 150°C to obtain high-purity zinc oxide. The method is an effective process for recovering zinc from waste water containing iron and zinc in a hot-dip galvanizing plant, and has the advantages of low equipment investment, low energy consumption, high purity of prepared products, environmental protection and no pollution, and the like.

Description

A method for extracting zinc from wastewater containing iron and zinc and preparing zinc oxide

technical field

The invention belongs to the technical field of waste resource treatment and relates to a method for extracting zinc from waste water containing iron and zinc and preparing zinc oxide.

Background technique

Zinc oxide is an oxide of zinc. Insoluble in water, soluble in acid and strong alkali. Zinc oxide is a commonly used chemical additive, widely used in the production of plastics, silicate products, synthetic rubber, lubricants, paint coatings, ointments, adhesives, food, batteries, flame retardants and other products. Zinc oxide has a large energy band gap and exciton binding energy, high transparency, and excellent room temperature light-emitting performance. It is used in liquid crystal displays, thin-film transistors, and light-emitting diodes in the semiconductor field. In addition, microparticles of zinc oxide, as a nanomaterial, have also begun to play a role in related fields.

Hot-dip galvanizing is a process technology in which steel, stainless steel, cast iron and other metals are immersed in molten liquid metal or alloy to obtain a coating. Hot-dip galvanizing is the most widely used steel surface treatment method with the best cost performance in the world today. Hot-dip galvanized products play an inestimable and irreplaceable role in corrosion reduction and life extension, energy saving and material saving of steel. At the same time, coated steel is also a high value-added short-term product supported and prioritized by the state. With the implementation of the western development strategy, the in-depth development of projects such as west-to-east power transmission, west-to-east gas transmission, south-to-north water diversion, the Three Gorges Project, rural power grids and urban power grids, the hot-dip galvanizing industry in my country has entered a new round of high-speed development. development stage.

At the same time, the iron-containing and zinc-containing wastewater produced by the hot-dip galvanizing plant is a kind of polluting industrial wastewater discharged from the pickling water of the hot-dip galvanizing plant workshop. Due to the different processes of each manufacturer, the iron content is usually 0.6g/L-3g/L Between L, zinc 0.1g/L～0.3g/L. The main pollutants contained in the wastewater are ferric chloride, ferrous chloride, zinc chloride, etc. In addition, most hot-dip galvanizing plants adopt the method of directly adding alkali and then pressing and purifying the wastewater. In this process, a large amount of iron will be produced. Zinc-containing and water-containing solid waste red mud. In addition to occupying a large amount of land during the stacking process, some chemical components in the red mud will infiltrate the land with water, which will easily cause the deterioration of the composition, structure and physical and chemical properties of the land. What's more serious is that the sewage generated by this high-zinc-containing waste seeps into the ground and easily causes groundwater pollution, causing heavy metal pollution in the groundwater, and also easily causing waste of resources.

So far, most of the methods for extracting zinc from wastewater are extraction methods to separate iron and zinc. The zinc-containing Fe ²⁺ solution is contacted with the extractant in countercurrent, and the mixture is extracted. The oil-water ratio is (1-4): 1, and the extraction time is After the extraction is completed, it is statically clarified for 16-20 minutes, and the oil is separated to obtain a zinc-containing loaded organic phase and a ferrous hydroxide solution with a zinc content of less than 1g/L.

Zinc hydroxide is prepared by stripping method, and its purity is relatively high. However, the process is cumbersome, the cost of industrialization is relatively high, the effect is not obvious for the solution with low zinc content, and the economic benefit is not high.

Contents of the invention

Aiming at the problems existing in the prior art, the present invention provides a method for extracting zinc from waste water containing iron and zinc and preparing zinc oxide. By adopting the present invention, the obtained solution containing iron and zinc is used to produce high-purity zinc oxide, and the waste water is Turn waste into treasure, eliminate the secondary pollution of waste water, and protect the ecological environment. Compared with the above, it is characterized by simple operation, low requirements for process equipment, and high-purity zinc oxide can be obtained by means of low cost.

In order to achieve the above object, technical scheme of the present invention is:

A method for extracting zinc and preparing zinc oxide from waste water containing iron and zinc, comprising the following steps:

Step 1, add lye

Under the condition of 15°C to 35°C, add lye to the wastewater containing iron and zinc, stir evenly, and adjust the pH value to 4-6.5 to obtain a solution containing zinc and iron, which contains hydroxide Ferrous iron; wherein, the mass percent concentration of the lye is 15% to 45%.

Step 2, low temperature oxidation

At room temperature, pass an oxidizing gas into the zinc-containing and iron-containing solution obtained in step 2 to oxidize part of Fe ²⁺ into Fe ³⁺ , and the oxidation time is 4-8 hours. When the solution turns yellowish brown, the oxidation is fully completed.

Step 3, filter to separate iron and zinc

The oxidized zinc-containing and iron-containing solution obtained in step 2 is filtered to obtain a filter cake and a zinc-containing solution; the filter cake is ferric hydroxide colloid.

Step 4, prepare zinc oxide

Adding alkaline substances to the zinc-containing solution obtained in step 3 at a temperature of 15° C. to 35° C. to adjust the pH value to 9-12 to obtain a white precipitate, which is filtered to obtain a filter cake and a filtrate. After the filter cake is fully washed, it is dried at 130°C to 150°C to obtain high-purity zinc oxide.

The iron-containing and zinc-containing wastewater is produced in the hot-dip galvanizing process, wherein the concentration of each component is: Fe: 0.6g/L-3g/L, Zn: 0.1g/L-0.3g/L, and the remainder The amount is water. In wastewater containing iron and zinc, the form of Fe element is ferric chloride and ferrous chloride, and the form of Zn element is zinc chloride, wherein the mixing ratio of each substance is any ratio.

The lye is sodium hydroxide, and its mass fraction is 15-45 wt%.

The oxidizing gas is oxygen or air, and the pressure thereof is 0.4-0.6 MPa.

Compared with the prior art, the beneficial effects of the present invention are: 1) The present invention can eliminate the secondary pollution of sludge, protect the ecological environment, and realize the resource recycling effect of waste reuse. 2) The present invention complies with my country's industrial policy of saving and reducing emissions, has small investment, low equipment requirements, and high iron-raising efficiency. 3) The present invention solves the problem of zero sludge pollution, and its process is a closed circuit, no waste liquid and residue will be generated, the operation is simple, and its process is short.

Detailed ways

The present invention will be described in further detail below in conjunction with embodiment.

The iron-containing and zinc-containing wastewater used in the following examples is produced in the hot-dip galvanizing production process, wherein the concentration is: Fe: 0.6g/L～3g/L, Zn: 0.1g/L～0.3g/L, the balance for water. In the wastewater containing iron and zinc, the Fe element exists in the form of ferric chloride and ferrous chloride, and the Zn element exists in the form of zinc chloride, wherein the mixing ratio of each substance is arbitrary.

Example 1

Get 2L of waste water and put it into a beaker, add 25ml of lye (15% by mass) to the waste water containing iron and zinc, adjust the pH value to 4.5, and obtain a solution containing ferrous hydroxide.

Oxygen is introduced into the ferrous hydroxide liquid, and the air pressure is 0.5MPa. Part of the Fe ²⁺ is oxidized to Fe ^{3 +} , and the oxidation time is 4 hours. During this process, continue to add 11ml of lye to keep the pH value at 5. If the solution turns yellowish brown, the oxidation is fully completed.

The oxidized zinc-containing and iron-containing solution is filtered to obtain a filter cake and a zinc-containing solution. The filter cake is ferric hydroxide colloid.

After washing the filter cake, dry it at 80°C for 6 hours, weigh it to 2.15g, and grind it to obtain high-purity iron oxide.

Add sodium hydroxide to the filtered zinc-containing solution to adjust the pH value to 10, and obtain a white precipitate, which is filtered to obtain a filter cake and a filtrate. High-purity zinc oxide can be obtained by drying 0.31 g of the filter cake at 130° C. for 4 hours.

Example 2

Take 2L of waste water and put it into a beaker, add 13ml of lye (30% by mass) to the waste water containing iron and zinc, and adjust the pH value to 5.5 to obtain a solution containing ferric hydroxide.

Oxygen is introduced into the ferrous hydroxide liquid, and the air pressure is 0.5MPa. Part of the Fe ²⁺ is oxidized to Fe ^{3 +} , the oxidation time is 4h, the solution turns from light green to yellowish brown, and the oxidation is fully completed.

The oxidized zinc-containing iron-containing solution is filtered to obtain a filter cake of ferric hydroxide colloid and a zinc-containing solution.

After washing the filter cake, dry it at 80°C for 6 hours, weigh it to 2.15g, and grind it to obtain high-purity iron oxide.

The filtered zinc-containing solution is added with lye to adjust the pH value to 9, and a white precipitate is obtained, which is filtered to obtain a filter cake and a filtrate. High-purity zinc oxide can be obtained by drying 0.34 g of the filter cake at 150°C for 4 hours.

Example 3

Take 2L of waste water and put it into a beaker, add 10ml of lye (45% by mass) to the waste water containing iron and zinc, and adjust the pH value to 6 to obtain a solution containing ferric hydroxide.

Air is introduced into the ferrous hydroxide liquid, and the air pressure is 0.4MPa. Part of the Fe ²⁺ is oxidized to Fe ^{3 +} , and the solution turns from light green to yellowish brown, indicating that the oxidation is fully completed.

The oxidized zinc-containing iron-containing solution is filtered to obtain a filter cake of ferric hydroxide colloid and a zinc-containing solution.

After the filter cake is washed, it is dried at 80° C. for 6 hours, and then ground to obtain high-purity iron oxide.

The filtered zinc-containing solution is added with lye to adjust the pH value to 12, and a white precipitate is obtained, which is filtered to obtain a filter cake and a filtrate. Dry the filter cake at 130°C to obtain high-purity zinc oxide.

Claims (8)

1. a method for extracting zinc and preparing zinc oxide from waste water containing iron and zinc, is characterized in that the following steps: Step 1, add lye Under the condition of 15°C to 35°C, add lye to the wastewater containing iron and zinc, stir evenly, and adjust the pH value to 4-6.5 to obtain a solution containing zinc and iron; the zinc-containing and iron-containing solution contains hydroxide Ferrous; Step 2, low temperature oxidation At room temperature, pass an oxidizing gas into the solution containing zinc and iron obtained in step 2, so that part of Fe ²⁺ is oxidized to Fe ^{3 +} , and the oxidation time is 4-8 hours; if the solution turns yellowish brown, the oxidation is fully completed ; Step 3, filter to separate iron and zinc Filtrating the oxidized zinc-containing and iron-containing solution obtained in step 2 to obtain a filter cake and a zinc-containing solution; the filter cake is ferric hydroxide colloid; Step 4, prepare zinc oxide Add alkaline substances to the zinc-containing solution obtained in step 3 at a temperature of 15°C to 35°C to adjust the pH value to 9-12 to obtain a white precipitate, which is filtered to obtain a filter cake and filtrate; after fully washing the filter cake, drying Dry to get zinc oxide. 2. the method for extracting zinc and preparing zinc oxide from a kind of waste water containing iron and zinc according to claim 1, is characterized in that, the waste water containing iron and zinc in said step 1 is produced in the hot-dip galvanizing production process , wherein the concentration of each component is: Fe: 0.6g/L ~ 3g/L, Zn: 0.1g/L ~ 0.3g/L, the balance is water; in wastewater containing iron and zinc, the presence of Fe element The form is ferric chloride and ferrous chloride, and the form of Zn element is zinc chloride, wherein the mixing ratio of each substance is any ratio. 3. The method for extracting zinc from wastewater containing iron and zinc and preparing zinc oxide according to claim 1 or 2, wherein the oxidizing gas is oxygen or air, and the pressure is 0.4-0.6 MPa. 4. The method for extracting zinc from wastewater containing iron and zinc and preparing zinc oxide according to claim 1 or 2, characterized in that the lye is sodium hydroxide with a mass fraction of 15-45 wt%. 5 . The method for extracting zinc from wastewater containing iron and zinc and preparing zinc oxide according to claim 3 , wherein the lye is sodium hydroxide, and its mass fraction is 15-45 wt%. 6. The method for extracting zinc from wastewater containing iron and zinc and preparing zinc oxide according to claim 1, 2 or 5, characterized in that the drying temperature in step 4 is 130°C-150°C. 7 . The method for extracting zinc from wastewater containing iron and zinc and preparing zinc oxide according to claim 3 , wherein the drying temperature in step 4 is 130° C. to 150° C. 8 . The method for extracting zinc from wastewater containing iron and zinc and preparing zinc oxide according to claim 4 , wherein the drying temperature in step 4 is 130° C. to 150° C.