Heavy metal solutions
1、Harm of heavy metals
Lead, cadmium, mercury, arsenic and other heavy metals, due to the development of industrial activities, cause enrichment in the human environment, enter the human body through the atmosphere, water, food, etc., accumulate in some organs of the human body, causing chronic poisoning and endangering human health. For example, cadmium can accumulate in the liver, kidney and other organs and tissues of the human body, causing damage to the organs and tissues. For example, from 1953 to 1961, in the Minamata disease event in Japan, inorganic mercury was converted into methylmercury in the sea water, which was absorbed and accumulated by fish and shellfish. After the biological amplification of the food chain, local residents were poisoned after eating.
2、Detection technology of heavy metals
Generally accepted methods for heavy metal analysis include colorimetry, UV, AAS, AFS, ICP, XRF and ICP-MS.
(1)Atomic Absorption Spectrometry -AAS
This method has become the main method for element quantitative analysis of inorganic compounds.
The process of atomic absorption analysis is as follows: 1. Make the sample into a solution (blank); 2. Prepare a series of correction solutions (standard samples) of analytical elements with known concentrations; 3. Measure the blank and the corresponding values of the standard samples in turn; 4. Draw the correction curve according to the corresponding values above; 5. Measure the corresponding values of unknown samples; 6. Determine the concentration of the sample according to the correction curve and the corresponding values of unknown samples Value.
（2） Ultraviolet visible spectrophotometry (UV)
The detection principle is: heavy metals and chromogenic agents, usually organic compounds, can react with heavy metals to form colored molecular groups. The color depth of the solution is directly proportional to the concentration. At a specific wavelength, colorimetric detection.
（3） Atomic fluorescence spectrometry (AFS)
Atomic fluorescence spectrometry is a method to determine the content of the elements to be measured by measuring the fluorescence emission intensity of the atomic vapor of the elements to be measured under the specific frequency radiation energy.
（4）X-ray fluorescence spectrometry (XRF)
X-ray fluorescence spectrometry is a method that uses the absorption of X-ray of sample to determine the composition of sample qualitatively or quantitatively according to the change of composition and its quantity. It has the characteristics of rapid analysis, simple sample pretreatment, wide range of analyzable elements, simple spectral lines, less spectral interference, variety of sample forms and non-destructive determination.
3、Control of heavy metal content in Montmorillonite
Because of the different testing principle, sensitivity and pretreatment of montmorillonite, the content of montmorillonite in the same sample with different analytical methods is different.
The company can customize montmorillonite products in depth to meet customers' requirements for heavy metal content under different test methods.
Montmorillonite is hygroscopic and can absorb 8-15 times of its own volume of water. It can expand after absorbing water, and the expansion ratio is more than 30 times of its original volume.
Montmorillonite is 2:1 layered silicate. Among them, Al3+ and Si4+ can be replaced by Mg2+, Ca2+ or Fe2+, and the exchangeable cation framework has residual negative charge. In addition, montmorillonite has weak interlayer binding force, which can adsorb cation and polar water molecules. According to the type of cation and relative humidity, one or two layers of water molecules can be adsorbed between layers. In addition, a certain amount of water molecules were also adsorbed on the surface of montmorillonite cells. Therefore, this kind of lattice extends along a-axis and b-axis, overlaps along c-axis, and the length of c-axis is not fixed. Wang Hongxi (1980) pointed out that when there is no water, the C 0 is 0.96nm. With the adsorption of different hydration cations between layers, different C axis lengths are produced. In the fully hydrated environment, the layer spacing can be increased. When a single montmorillonite crystal cell contains two H2O molecules, the length of C axis is 1.24nm; when there are four H2O molecules, the length of C axis is 1.54nm; in the higher stage of hydration, the length of C axis is 1.84-2.14nm. Therefore, the volume of montmorillonite can be increased by 10-30 times, and the water absorption of Na montmorillonite is stronger than that of Ca montmorillonite. It can be seen that the expansion of montmorillonite is driven by exchangeable cations and hydration energy at the bottom of crystal layer.
The water absorption of montmorillonite is limited to a certain extent. When the water molecular layer (i.e. hydration membrane) absorbed reaches a certain thickness and is evenly distributed, the water absorption reaches a balance. If the balance is destroyed, the water absorption and expansion performance can be restored.
The swelling and drying shrinkage of montmorillonite (including the escape of a small amount of structural water) are reversible under certain conditions. However, it is difficult to re absorb water after the interlayer water is completely lost. After drying at high temperature, the ability of rehydration is completely lost. The temperature of Ca montmorillonite losing hydration ability is 300-390 ℃, and that of Na montmorillonite is 390-490 ℃.
The moisture test method of montmorillonite is to take about 1g of evenly mixed sample, put it into a flat weighing bottle that is dried to constant weight and precisely weighed; then put it into an oven or dryer at 105 ℃ for drying for at least 2 hours. Dry to constant weight, cool to room temperature, then weigh. The water content of the test article is calculated from the weight loss and sampling amount.
The company can customize montmorillonite products with different moisture requirements according to customer requirements, and adopt professional moisture-proof and moisture-proof packaging to ensure the product moisture stability.
Due to the content change of iron, calcium, manganese and sodium ions in the lattice structure, the raw montmorillonite ore presents various colors like white, light gray, light pink, brick red, light green and dark purple, presents wax like luster and soap like fracture, and has good adsorption, suspension, colloid dispersion, adhesion and ion exchange.
Because of the different formation conditions of the deposits, the gradual change of the ore bed and the distribution change of the metal ions (mainly Na +, Ca2 +, Fe3 +, Mn2 +) between the double octahedron layers, the appearance color of the montmorillonite will also change. Color stability is also an important guarantee of product stability.
The company selects high-quality ore sources from all parts of the country, strictly checks the primary separation of raw ore, and enters the next process only after the indicators such as montmorillonite content and ion exchange capacity are qualified. Therefore, there is no direct relationship between the color, content and grade of montmorillonite of our company. At the same time, we can also provide different color montmorillonite products for our customers to meet their needs.