CN103754978B - A method of selective adsorption and separation of lead ions using KNbWO6 - Google Patents

Abstract

The invention discloses a method for selectively adsorbing and separating heavy metal lead ions by using pyrochlore-structured KNbWO ₆ ·H ₂ O. Add potassium niobate tungstate into water, stir for 20-50 hours at pH 4-5.5, and centrifuge to separate the solid and clear liquid; the dosage of potassium niobate tungstate is calculated as 0.2-0.6 g/L based on the volume of water. KNbWO ₆ ·H ₂ O can adsorb and separate lead ions through ion exchange, and has good selectivity for the adsorption of lead ions. The method of the present invention is simple and efficient, and has a good effect on the separation and adsorption of heavy metal lead ions, and can be applied to the removal of heavy metal lead in waste water and the separation of lead ions in complex systems, and the potassium niobate tungstate after the lead ion adsorption can be used Nitric acid exchange regeneration, reuse.

Description

A method of selective adsorption and separation of lead ions using KNbWO6

technical field

The invention belongs to the technical field of adsorption and separation of heavy metals, and relates to the application of an inorganic ion exchanger for the adsorption and separation of lead ions in sewage and wastewater.

Background technique

Heavy metal pollution from mining, exhaust emissions and use of metal products has become an important issue affecting human health. Lead is a very common and highly toxic heavy metal pollutant, which can be polluted in processes such as metal plating, crude oil refining, paint and pigment industry, and battery production. Inorganic lead and its compounds in the environment are very stable and difficult to metabolize and degrade. Exposure to lead will have adverse effects on human organs, especially the lungs, kidneys, reproductive system, and cardiovascular system. Due to the toxicity and pollution characteristics of lead, the standard value of lead in the environment is very high, especially the western developed countries have strict restrictions on the use of lead. China's latest "Drinking Water Sanitation Standard" in 2012 requires that the lead content is More than 0.01mg/L.

Effective methods to efficiently remove heavy metal ions such as lead in sewage are very important for protecting the environment and human health. There are many methods for treating heavy metal ions in wastewater, such as: reductive deposition, evaporation, electrochemical reduction, adsorption and direct sedimentation. Adsorption is considered to be an efficient and economical method for treating heavy metal ions in sewage, including activated carbon and other adsorbents that can be used to remove heavy metal ions in sewage. Inorganic materials such as natural or artificial zeolites, metal ferrocyanides and ferricyanides, layered compounds, transition metal hydrated oxides and hydroxides can also be used as adsorbents for heavy metal ions. In recent years, it has been reported that titanate nanostructures (J.Phys.Chem.C., 112, 16275-16280, 2008) and titanate-ferric oxide complexes (J.Mater.Chem.A., 1,805-813,2013) as an adsorbent for lead ions; layered manganese oxides are also used as adsorbents for lead ions (J.Hazard.Mater.,196,318-326,2011).

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for adsorbing and separating lead ions by using pyrochlore structure niobium tungstate KNbWO ₆ through ion exchange, which is different from the prior art.

_Pyrochlore ^{- structured} potassium niobate tungstate has ^good _selectivity for ^the adsorption of lead ion Pb ²⁺ . When the solution was subjected to adsorption experiments, it was found that the presence of three ions, Cd ²⁺ , Co ²⁺ , and Mn ²⁺ , had no significant effect on the adsorption effect of lead ions. The niobium tungstate after adsorbing lead ions can be regenerated by nitric acid exchange and reused. The method of the invention is simple and efficient, has a good effect on the separation and adsorption of the heavy metal lead, and can be used for the removal of heavy metals in sewage and the separation of lead ions in complex systems.

Concrete technical scheme is as follows.

A method for selective adsorption and separation of lead ions using KNbWO ₆ , adding potassium niobate tungstate (KNbWO ₆ ·H ₂ O) to water, stirring at pH 4-5.5 for 20-50 hours, and centrifuging to separate the solid and clear liquid; niobium The dosage of potassium tungstate is 0.2-0.6 g/L calculated by volume of water.

The potassium niobate tungstate mentioned above is KNbWO ₆ ·H ₂ O with pyrochlore structure.

The preferred ion exchange condition is that the dosage of potassium niobate tungstate is 0.4-0.5 g/liter calculated by volume of water, and the mixture is stirred for 48-50 hours at a pH value of 5-5.5. Potassium niobate tungstate dosage greater than 0.5 g/L is also very effective, but more than 0.6 g/L is wasted.

The pH can be adjusted with nitric acid at a concentration of 0.1 mol/L.

The increase of temperature contributes to the improvement of the adsorption rate of Pb ²⁺ ions. But for the adsorption and separation of Pb ²⁺ ions in wastewater, most of them are carried out at room temperature.

The present invention proposes for the first time to use potassium niobate tungstate to adsorb and separate lead ions through ion exchange. This method of adsorbing and separating lead ions using ion exchange is completely different in principle from the existing method of using surface adsorption to adsorb and separate lead ions; the present invention The method is simple and efficient; pyrochlore-structured KNbWO ₆ ·H ₂ O has a very good effect on the separation and adsorption of heavy metal lead ions, and the adsorption rate is above 75%. The inductively coupled plasma (ICP ) analysis test, using the Langmuir isotherm adsorption equation for fitting calculation, the KNbWO ₆ ·H ₂ O sample has a pH value of 5.0, and the maximum adsorption capacity of lead ions in the lead nitrate solution is 86.95 mg/g; In the pore structure of KNbWO ₆ ·H ₂ O with a green stone structure, lead ions are separated by ion exchange adsorption, and the adsorption of lead ions has better selectivity, which can avoid other impurities in the complex system from affecting the adsorption effect; this paper The invention can be applied to the removal of heavy metal lead (lead ions) in sewage and the separation of lead ions in complex systems. Potassium niobium tungstate after adsorbing lead ions can be regenerated by nitric acid exchange and reused.

Description of drawings

Figure 1 is the fitting model of the Langmuir isotherm adsorption curve for potassium niobate tungstate KNbWO ₆ ·H ₂ O exchanging lead ions.

Fig. 2 is the time-varying curve of ion exchange adsorption efficiency in Example 2. where the ion exchange efficiency is:

The ordinate is the remaining lead ion concentration in the solution after exchange.

Figure 3 shows the ion exchange adsorption efficiency of potassium niobate tungstate KNbWO ₆ ·H ₂ O on 50 mg/L lead nitrate solution and the comparison of lead ion exchange adsorption results when lead nitrate coexists with cobalt nitrate, manganese chloride and cadmium chloride solutions.

Detailed ways

Example 1

Prepare 50 milliliters of lead nitrate solutions with concentrations of 20, 30, 40, 50, 60, 80, 90, and 100 mg/L, adjust the pH value of the solution to 5.0 with 1 mol/L of nitric acid, and mix 20 mg/L of KNbWO ₆ ·H ₂ O with a pyrochlore structure was added to the above 50 ml lead nitrate solution, and after 48 hours of ion exchange time under the action of magnetic stirring, the solid-liquid was separated by centrifugation, and the obtained clear liquid was inductively coupled plasma (ICP ) for lead ion concentration analysis. The measured experimental results were fitted with the Langmuir isotherm adsorption equation, and the equilibrium concentration Ce (mg/L) was plotted against Ce/Qe (gram/L, Qe is the equilibrium adsorption amount), and it was found that the Langmuir isotherm The adsorption curves fit the isotherm data well.

Figure 1 shows the Langmuir isotherm adsorption curve fitting curve data.

Example 2

Prepare a 30 mg/L lead nitrate solution, adjust the pH of the solution to 5.0 with 1 mol/L nitric acid, and add 20 mg of pyrochlore-structured KNbWO ₆ ·H ₂ O to the above 50 ml lead nitrate solution at room temperature After 48 hours of ion exchange time under the action of magnetic stirring, the solid and liquid were separated by centrifugation, and the obtained clear liquid was analyzed for lead ion concentration by inductively coupled plasma (ICP).

After 48 hours of ion exchange, the ion exchange efficiency was 99.0%. Figure 2 shows the time-dependent curve of the ion exchange adsorption efficiency of potassium niobate tungstate KNbWO ₆ ·H ₂ O to 30 mg/L lead nitrate solution. It can be seen from Figure 2 on the right that under the conditions of this example, the ion exchange time is 20 hours, and the ion exchange efficiency is 88.7%.

Example 3

Prepare a 50 mg/L lead nitrate solution, adjust the pH of the solution to 5.0 with 1 mol/L nitric acid, and add 20 mg of pyrochlore-structured KNbWO ₆ ·H ₂ O to the above 50 ml lead nitrate solution at room temperature After 48 hours of ion exchange time under the action of magnetic stirring, the solid and liquid were separated by centrifugation, and the obtained clear liquid was analyzed for lead ion concentration by inductively coupled plasma (ICP).

Compared with Example 2, increasing the initial concentration of lead ions, the ion exchange efficiency was 76.2%.

Example 4

Prepare a 30 mg/L lead nitrate solution, adjust the pH of the solution to 4.0 with 1 mol/L nitric acid, and add 20 mg of pyrochlore-structured KNbWO ₆ ·H ₂ O to the above 50 ml lead nitrate solution at room temperature After 48 hours of ion exchange time under the action of magnetic stirring, the solid and liquid were separated by centrifugation, and the obtained clear liquid was analyzed for lead ion concentration by ICP.

Compared with Example 2, the reaction pH value decreased, and the ion exchange efficiency decreased.

Example 5

Prepare a 30 mg/L lead nitrate solution, adjust the pH of the solution to 5.5 with 1 mol/L nitric acid, and add 20 mg of pyrochlore-structured KNbWO ₆ ·H ₂ O to the above 50 ml lead nitrate solution at room temperature After 48 hours of ion exchange time under the action of magnetic stirring, the solid and liquid were separated by centrifugation, and the obtained clear liquid was analyzed for lead ion concentration by ICP.

Compared with Example 2, the reaction pH value increases, but the ion exchange efficiency does not change significantly.

Example 6

Prepare a 30 mg/L lead nitrate solution, adjust the pH of the solution to 5.0 with 1 mol/L nitric acid, and add 20 mg of pyrochlore-structured KNbWO ₆ ·H ₂ O to the above 50 ml lead nitrate solution at room temperature After 10 hours of ion exchange time under the action of magnetic stirring, the solid and liquid were separated by centrifugation, and the obtained clear liquid was analyzed for lead ion concentration by ICP.

Compared with Example 2, the ion exchange time is shortened, and the ion exchange efficiency decreases. The ion exchange time is 10 hours and the ion exchange efficiency is about 67%.

Example 7

Prepare a 30 mg/L lead nitrate solution, adjust the pH of the solution to 5.0 with 1 mol/L nitric acid, and add 20 mg of pyrochlore-structured KNbWO ₆ ·H ₂ O to the above 50 ml lead nitrate solution at room temperature After 50 hours of ion exchange time under the action of magnetic stirring, the solid and liquid were separated by centrifugation, and the obtained clear liquid was analyzed for lead ion concentration by ICP.

Compared with Example 2, the ion exchange efficiency does not change when the ion exchange time is prolonged.

Example 8

Prepare a 30 mg/L lead nitrate solution, adjust the pH of the solution to 5.0 with 1 mol/L nitric acid, and add 10 mg of pyrochlore-structured KNbWO ₆ ·H ₂ O to the above 50 ml lead nitrate solution at room temperature After 48 hours of ion exchange time under the action of magnetic stirring, the solid and liquid were separated by centrifugation, and the obtained clear liquid was analyzed for lead ion concentration by inductively coupled plasma (ICP).

Compared with Example 2, reducing the amount of KNbWO ₆ ·H ₂ O reduces the ion exchange efficiency.

Example 9

Prepare a 30 mg/L lead nitrate solution, adjust the pH of the solution to 5.0 with 1 mol/L nitric acid, and add 30 mg of pyrochlore-structured KNbWO ₆ ·H ₂ O to the 50 ml lead nitrate solution at room temperature After 48 hours of ion exchange time under the action of magnetic stirring, the solid and liquid were separated by centrifugation, and the obtained clear liquid was analyzed for lead ion concentration by inductively coupled plasma (ICP).

Compared with Example 2, increasing the amount of KNbWO ₆ ·H ₂ O does not change the ion exchange efficiency.

Example 10

Prepare a 30 mg/L lead nitrate solution, adjust the pH of the solution to 5.0 with 1 mol/L nitric acid, and add 20 mg of pyrochlore-structured KNbWO ₆ ·H ₂ O to the above 50 mL of nitric acid after the system is heated to 90°C In the lead solution, after 2 hours of ion exchange time under the action of magnetic stirring, the solid and liquid were separated by centrifugation, and the obtained clear liquid was analyzed for lead ion concentration by inductively coupled plasma (ICP).

The ion exchange time is only 2 hours, and the ion exchange efficiency is 100%. Compared with Example 2, the ion exchange efficiency is obviously improved when the temperature is raised.

Example 11

In order to investigate the effect of pH value on the adsorption effect of KNbWO ₆ ·H ₂ O ions, the adsorption effect experiment with the same conditions was carried out. Five parts of lead nitrate solution with an initial concentration of 50 mg/L were prepared 50 mL, and the solutions were adjusted with 1 mol/L nitric acid respectively. The pH values are 2, 3, 4, 5.0, 5.5. At room temperature, 20 mg of pyrochlore-structured KNbWO ₆ ·H ₂ O is added to the above lead nitrate solution, and after 30 hours of ion exchange time under the action of magnetic stirring, The solid and liquid were separated by centrifugation, and the resulting clear liquid was analyzed for lead ion concentration by inductively coupled plasma (ICP).

Table 1 shows the effect of potassium niobate tungstate KNbWO ₆ ·H ₂ O on the lead ion exchange in lead nitrate solution under different pH values.

The experimental results show that the pH value is 5.0 and 5.5 lead ion adsorption effect is good, the pH value is greater than 5.5 the adsorption effect has a downward trend.

Table 1

Example 12

In order to investigate the selective adsorption effect of KNbWO ₆ ·H ₂ O ions, a selective adsorption experiment was carried out: the concentration of lead nitrate was 50 mg/L, the concentration of cobalt nitrate was 50 mg/L, the concentration of manganese chloride was 50 mg/L, and the concentration of chlorine 50 milliliters of the mixed solution with a cadmium chloride concentration of 50 mg/liter, adjust the pH value of the solution between 5.0 and 5.5 with 0.1 mol/liter nitric acid, add 20 milligrams of the KNbWO ₆ ·H ₂ O sample with a pyrochlore structure, under room temperature Stir for 30 hours, centrifuge to separate the solid and the supernatant, and analyze the supernatant by inductively coupled plasma (ICP). The ion exchange efficiencies of Mn ²⁺ , Cd ²⁺ , Co ²⁺ and Pb ²⁺ are 7.2%, 0.6%, respectively. 21.2% and 78.6%.

The ion exchange adsorption efficiency of potassium niobate tungstate KNbWO ₆ ?H ₂ O on 50 mg/L lead nitrate solution and the comparison of lead ion exchange adsorption results when lead nitrate coexists with cobalt nitrate, manganese chloride and cadmium chloride solution, see Figure 3 .

Compared with Example 3, KNbWO ₆ ·H ₂ O still maintains a high ion exchange efficiency for Pb ²⁺ under the condition of simultaneous presence of several ions, and has good selectivity for Pb ²⁺ .

Claims (3)

1. A method of using KNbWO ₆ to selectively adsorb and separate lead ions. Add potassium niobate tungstate to water, stir for 20 to 50 hours at a pH value of 4 to 5.5, and centrifuge to separate the solid and clear liquid; the amount of potassium niobate tungstate is based on water The calculated volume is 0.2-0.6 g/L; the potassium niobate tungstate is KNbWO ₆ ·H ₂ O with a pyrochlore structure. 2. The method for utilizing _KNbWO6 to selectively adsorb and separate lead ions according to claim 1, characterized in that, in the method for adsorbing and separating lead ions, the amount of potassium niobate tungstate is calculated as 0.4 to 0.5 grams per liter according to the volume of water , stirred at pH 5-5.5 for 48-50 hours. 3. The method for utilizing KNbWO ₆ to selectively adsorb and separate lead ions according to claim 1 or 2, characterized in that the pH value is adjusted with nitric acid with a concentration of 0.1 mol/liter.