CN102621258B - A kind of heavy metal chromium form fractionation method - Google Patents

Abstract

The present invention adopts dolomite as the adsorption material for the first time, and is used for the separation of Cr(VI) and Cr(III) in the natural water environment. A series of experiments show that the adsorption rate of dolomite (80‑100 mesh) in natural water bodies is greater than 95% for Cr(III), while the adsorption rate for Cr(VI) is less than 5%. The adsorbent used in the method is natural mineral, which is cheap and convenient to obtain materials, and the separation method adopted is simple and fast, and the separation effect is remarkable. Therefore, this method can be used for the speciation separation of Cr(III) and Cr(VI) in water.

Description

A kind of heavy metal chromium form separation method

technical field

The invention relates to the field of environmental analysis, in particular to a method for separating forms of heavy metal chromium.

technical background

Chromium (Cr) mainly exists in the environment in two forms: trivalent Cr(III) and hexavalent Cr(VI). These two forms of Cr have obvious differences in chemical properties, biological activities and toxicological levels. Cr(VI) mainly exists in the form of anion CrO ₄ ^2- and Cr ₂ O ₇ ^2- , which has high chemical activity, high solubility and high toxicity, and is easy to cause harm to animals, plants and humans. It is confirmed by the World Health Organization carcinogens. On the contrary, Cr(III) is an essential trace element in the process of carbohydrate and fat metabolism. An appropriate amount of Cr(III) can reduce blood sugar concentration in plasma and improve the body’s ability to respond to stress. The lack of Cr(III) in the human body will cause Disorders of glucose metabolism, leading to abnormal glucose tolerance and diabetes. Due to the obvious differences in the impacts of different forms of Cr on the environment and human health, the speciation analysis of Cr is of great significance in environmental chemistry, life science, and physiological medicine.

However, among the current Cr element detection instruments, only inductively coupled plasma mass spectrometer (ICP-MS) can directly detect the concentration of Cr(VI) and Cr(III) in solution. However, the detection cost of ICP-MS is relatively high, and it is not suitable for the detection of a large number of samples. In order to enable other instruments (such as atomic absorption spectrometry AAS) to detect Cr(VI) and Cr(III) in solution, the two forms of Cr can only be separated before detection, so that only one form of Cr exists in the solution. Cr (ie Cr(III) or Cr(VI)), and then measure the Cr concentration in each component after separation. Therefore, the separation of Cr(VI) and Cr(III) in solution becomes the key to rapid and accurate detection of their concentration.

Solid phase extraction (SPE) is a commonly used separation and purification method, which has the characteristics of high extraction efficiency, good selectivity, wide application range, simple operation and time saving. Solid-phase extraction has been widely used in the study of the speciation separation of Cr, and the separation materials used include resins, fibers, metal oxides, biosorbent materials, and new nanomaterials. Although the above materials can satisfy the requirements for the separation of Cr forms, most of them have the disadvantages of scarce raw materials, complicated preparation, and high price, which are not conducive to large-scale use. Therefore, it is urgent to find a natural adsorbent with simple separation method and excellent separation effect for the separation of Cr(III) and Cr(VI). Dolomite (CaMg(CO ₃ ) ₂ ) is a natural mineral that is ubiquitous in nature, cheap and easy to obtain. Dolomite has been used to adsorb and remove Cu, Pb, As and other heavy metal ions in environmental samples, and it has also been used for the adsorption of Cr(VI) after heat treatment. However, the adsorption of Cr(III) on dolomite has not been reported yet.

The present invention adopts dolomite as the adsorption material for the first time, and is applied to the separation of Cr(VI) and Cr(III) in actual water bodies. Through a series of experiments, combined with graphite furnace atomic absorption spectroscopy (GFAAS) as a detection method, it was proved that natural dolomite has a good adsorption effect on Cr(III) and almost no adsorption on Cr(VI). The present invention aims to provide a more convenient, economical and rapid method for the speciation analysis of Cr.

Contents of the invention

The main contents of the present invention and the characteristics of the present invention are clarified by the following description.

The invention relates to a method for separating forms of heavy metal chromium. The method uses natural dolomite as the adsorption material, and experiments have proved that the adsorbent has an obvious adsorption effect on Cr(III) and almost no adsorption on Cr(VI). Therefore, it can be used for the separation of Cr(VI) and Cr(III) in water. The adsorbent used in the invention has wide sources and low price, and the separation method used is simple and easy to operate, and can overcome the defects of the existing Cr form separation method.

Concrete content of the present invention is as follows:

(1) First, crush and sieve the large-grained dolomite, and select particles with a particle size between 80-100 mesh for the experiment.

(2) Put a layer of filter paper on the bottom of the 15mL SPE column, and connect a 200μL pipette tip to the water outlet of the column; weigh 4g of dolomite particles in (1), fill in the column, and Spread a small amount of silk floss on the upper layer to prevent the particles from floating up.

(3) Prepare a stock solution of Cr(III) with deionized water and CrCl ₃ 6H ₂ O, and prepare a stock solution of Cr(VI) with deionized water and K ₂ CrO ₄ , the concentration is 1000mg/L, and the ionic strength 0.05mol/L NaClO ₄ , and added 0.1% (v/v) HNO ₃ , stored at low temperature until use. Working solutions were prepared by diluting the above stock solutions with deionized water. Use _HClO4 and NaOH to adjust the desired pH.

(4) Prepare an appropriate amount of Cr(III) and Cr(VI) working solution by diluting the stock solution with deionized water, and adjust its pH=7.0±0.5, take 12mL of working solution and flow through the prepared dolomite SPE column (natural flow rate =0.7mL/min), collect the effluent and measure the pH value.

(5) Select two kinds of actual chromium-containing wastewater, electroplating wastewater and chromium slag extract, and adjust its pH=7.0±0.5, take 12mL of working solution and flow through the prepared dolomite SPE column (natural flow rate=0.7mL/min), The effluent was collected and the pH was measured.

(6) The concentrations of total Cr and Cr(VI) in the solution before and after adsorption were detected by atomic absorption spectrometry (AAS) and spectrophotometer, respectively. The concentration difference between Total Cr and Cr(VI) in the solution is the amount of Cr(III) adsorbed by dolomite.

Description of drawings

Accompanying drawing 1 is the photoelectron spectrum (EDX) of adsorbent dolomite, it can be seen from the spectrum that the used dolomite mainly contains calcium, magnesium, carbon, oxygen and other elements, which is consistent with its chemical formula CaMg(CO ₃ ) ₂ .

Accompanying drawing 2 is the effect of pH value on the adsorption rate of Cr(VI) and Cr(III) on dolomite. It can be seen that in the interval of pH 4-10, the adsorption rate of dolomite to Cr(III) is greater than 95%, while the adsorption rate to Cr(VI) is lower than 5%, indicating that the adsorbent can be used for Separation of Cr(VI) and Cr(III) in water.

Accompanying drawing 3 is the influence that common substance in water body has on adsorption effect. It can be seen from the figure that Mg ²⁺ , Ca ²⁺ and HA (humic acid) have no effect on the adsorption effect; carbonate (CO ₃ ^2- ) and acetic acid HAc do not affect the adsorption effect at low concentrations, and when the concentration is greater than 0.05mol L ^-1 will affect the adsorption effect. In natural water bodies, there is almost no acetic acid (this is because the chromium slag extract contains acetic acid in the actual sample below), and the background value of carbonic acid is also lower than 0.05mol/L. Therefore, the experimental results show that the main substances in the water have no obvious influence on the adsorption effect.

Accompanying drawing 4 is the adsorption capacity of dolomite Cr (III). It can be seen from the figure that when the concentration of Cr(III) is below 10mg/L, it can be almost completely adsorbed by dolomite, and the maximum adsorption capacity is 0.03mg/kg.

Accompanying drawing 5 is the adsorption penetration of dolomite to Cr (III) solution in the continuous flow process. 16g of dolomite is packed into a small column (diameter 1.1cm, length 21cm). Use a pump at a flow rate of 0.7mL/min to continuously feed a 500μg/L Cr(III) solution prepared with tap water (add 0.05mol/L NaClO ₄ ), and then measure the concentration of Cr(III) after adsorption through regular sampling. It can be seen from the above examples that 16 g of dolomite can absorb at least 25 L of Cr(III) solution with a concentration of 500 μg/L before the concentration of the effluent is higher than the national drinking water chromium standard of 100 μg/L. It shows that this method can effectively intercept Cr(III) in the solution.

detailed description

The present invention is further illustrated below through examples.

Example 1 Add 30 μg/L Cr(III) and 20 μg/LCr(VI) to tap water, well water and river water respectively, and only add 1000 μg/L Cr(III) to electroplating wastewater and chromium slag extract. Use dolomite to separate Cr(III) and Cr(VI) from the above actual water samples: take 12mL water samples respectively, and absorb them in SPE cartridges with 4g dolomite at a flow rate of 0.7mL/min. The concentration of total Cr before adsorption (that is, the concentration of Cr(III) and Cr(VI) included in Total Cr) and the concentration of Cr(III) after adsorption were measured by graphite furnace atomic absorption spectrometry (GFAAS). Then use a spectrophotometer to detect the concentration of Cr(VI) after adsorption at a wavelength of 540 nm. The result of the experiment was that Cr(III) was not detected after adsorption, but the amount of Cr(VI) measured was consistent with that before adsorption (Table 1). Therefore, this example illustrates that the present invention has a remarkable effect on the separation of Cr(III) and Cr(VI).

Table 1. Dolomite separation of Cr(III) and Cr(VI) in real water samples.

^a means not detected;

^b means not added.

Claims (1)

1. a heavy metal chromium form fractionation method, it is characterised in that step is as follows:

(1) particle diameter natural dolomite between 80-100 mesh is first selected；

(2) at the SPE little column bottom pad last layer filter paper of 15mL, and one 200 is connect at the outlet of pillar μ L liquid-transfering gun rifle head；Weigh dolomite particles in 4g step (1), be filled in pillar, and Spreading a small amount of silk floss on upper strata prevents granule from floating；

(3) with deionized water and CrCl₃·6H₂The storing solution of O preparation Cr (III), with deionized water and K₂CrO₄ The storing solution of preparation Cr (VI), concentration is 1000mg/L, and ionic strength is 0.05mol/L NaClO₄, and Add 0.1% (v/v) HNO₃, cryopreservation is stand-by；

(4) prepared appropriate Cr (III) and Cr (VI) working solution by deionized water dilution storing solution, and regulate it PH=7.0 ± 0.5, takes the 12mL treatment fluid flow dolomite SPE post through preparing, natural flow velocity=0.7mL/ Min, collects effluent and measures pH value, uses HClO₄Required pH value is regulated with NaOH；

(5) choose electroplating wastewater and two kinds of actual chromate waste waters of chromium slag extract, and regulate its pH=7.0 ± 0.5, Take the actual chromate waste water of 12mL and flow through the dolomite SPE post prepared, natural flow velocity=0.7mL/min, receive Collection effluent also measures pH value；

(6) total Cr of detecting respectively before and after absorption in solution with atomic absorption spectrography (AAS) and spectrophotometer and The concentration of Cr (VI)；Achieve trivalent chromium and chromic separation in water body.