The invention can be used in inorganic chemistry. A method of obtaining crystalline cadmium sulfide includes placing sulfate-reducing bacteria in a synthetic medium containing metals, and adding nutrients, including solutions of vitamins, salts, and cofactors. During cultivation, the sulfate-reducing bacteria Desulfovibrio sp. A2, and a synthetic medium containing a cadmium ion source - cadmium chloride solution. The concentration of cadmium ions in the synthetic medium is 150 mg / l. Aluminum foil is placed in a cultivation vessel, cultivation is carried out at a temperature of 28 ° C for 18 days. Collected from the foil and from the bottom of the bottle, the precipitate containing cadmium sulfide crystals is dried. The invention makes it possible to obtain cadmium sulfide from wastewater and liquid waste from metallurgical enterprises. 2 dwg, 3 tbl, 1 ex

Drawings to the RF patent 2526456

The invention relates to a method for producing pure cadmium sulfide (CdS) from solutions containing metals using sulfate-reducing bacteria (CRB).

The proposed method can be used to obtain pure cadmium sulfide from wastewater containing metal ions, including cadmium, and liquid waste from mining and processing metallurgical enterprises. When applying the proposed method, it is possible to selectively precipitate cadmium in the form of sulfides. This feature allows using liquid waste from metallurgical enterprises and waste water as a secondary source of raw materials for the production of cadmium sulfides. Cadmium sulfide is used in semiconductor lasers, is a material for the manufacture of solar cells, solar cells, photodiodes, light-emitting diodes, phosphors, pigments for artistic paints, glass and ceramics. Cadmium sulfide pigments are valued for their good temperature stability in many polymers such as engineering plastics. By replacing some of the sulfur atoms with selenium in CdS crystals, a wide variety of dye colors from green-yellow to red-violet can be obtained. Cadmium sulfide is a wide gap semiconductor. This property of CdS is used in optoelectronics, both in photodetectors and in solar cells. Scintillators are made from single crystals of cadmium sulfide for registration of elementary particles and gamma radiation.

In nature, cadmium sulfide exists as the minerals greenockite and howliite, which occur as yellow deposits on sphalerite (ZnS) and smithsonite. Since these minerals are not widespread in nature, cadmium sulfide is obtained by synthesis for industrial use and scientific and technical work.

Cadmium sulfides are obtained by chemical methods - heating sulfur with cadmium or passing hydrogen sulfide over cadmium, oxide or cadmium chloride when heated. A known method of producing powdered cadmium and lead sulfides (RF patent, No. 2203855, C01G 11/02, C01G 21/21, 2003). The invention relates to methods for producing powder materials in molten salts. The synthesis is carried out in a molten medium. The molten medium is formed by crystalline thiourea, and includes anhydrous cadmium or lead acetates as a metal-containing component. The synthesis is carried out by mixing powders of one of the indicated salts and thiourea with a 2-4-fold molar excess of thiourea and further holding at 160-180 ° C for 20-30 minutes. The practical yield of products obtained by the proposed method is over 95%. In addition, they contain an admixture of elemental sulfur (3-4 wt%), which, depending on the further use of the product, can be removed by washing with an organic solvent (toluene, carbon tetrachloride, etc.). The disadvantages of this method are the energy consumption of production, the need to use special, expensive equipment. In addition, chemical production negatively affects the condition environment.

The formation of cadmium sulfide crystallites on the cell surface by bacteria Klebsiella pneumonia and Clostridium thermoaceticum is known (Aiking H. et al. Detoxification of mercury, cadmium, and lead in Klebsiella aerogenes NCTC 418 growing in continuous culture // Appi Environ Microbiol. 1985 Nov; 50 (5 - P. 1262-1267; PR Smith et al. PHOTOPHYSICAL AND PHOTOCHEMICAL CHARACTERIZATION OF BACTERIAL SEMICONDUCTOR CADMIUM-SULFIDE PARTICLES // Journal of the Chemical Society. Faraday transactions. - 1998, 94 (9). - pp. 1235-1241 ).

CdS crystallites synthesized on the surface of K. pneumonia bacteria effectively absorb UV light, which protects the bacterium from its harmful effects. Deep-sea marine fluorescent bacterium Pseudomonas aeruginosa removes cadmium from the medium by the formation of CdS crystallites on the cell wall (Wang CL et al. Cadmium removal by a new strain of Pseudomonas aeruginosa in aerobic culture // Appl. Environ. Microbiol. - 1997, 63. - pp. .4075-4078). The sizes of cadmium sulfide crystallites vary from tens of microns outside cells to tens of angstroms inside cells or on their surface. Crystallites of cadmium sulfide are formed only under certain conditions for organisms to tolerate unfavorable environmental conditions.

The closest in essence and the achieved result to the claimed invention is a method for removing low concentrations of cadmium ions using a bioreactor with sulfate-reducing bacteria (Hiroshi H. et al. Removal of Low Concentrated Cadmium Ions Using Fixed-bed Sulfate-Reducing Bioreactor with FS Carrier // Journal of the Mining and Materials Processing Institute of Japan. - 2003. - V.119, No. 9. - pp.559-563). The recovery of heavy metal ions from water took place in a bioreactor using sulfate-reducing bacteria immobilized on a fibrous slag, which was used as a biocarrier. In this process, sulfate ions in the liquid are biologically converted to hydrogen sulfide (H 2 S), which reacts with metal ions to form ultrafine metal sulfide particles. Then the formed particles collect on the surface of the carrier in the upper part of the reactor, as a result of which heavy metal ions and their sulfides accumulate. With continuous treatment of water contaminated with 6 mg / L cadmium, almost complete removal was carried out over a period of about 30 days.

The disadvantage of this method is that its use is possible only at low concentrations of cadmium ions in the medium and crystalline cadmium sulfide is not formed.

The objective of the present invention is to develop a method for obtaining crystalline cadmium sulfide from solutions with an increased content of cadmium ions (up to 150 mg / l), not containing impurities of other metal sulfides, using sulfate-reducing bacteria resistant to increased concentrations of cadmium ions.

The task is solved by placing CRB highly resistant to cadmium ions into a synthetic medium simulating wastewater containing metals, with the addition of nutrients, including solutions of vitamins, salts, cofactors, lactate, sodium sulfide, with further cultivation in a thermostat and drying, but , in contrast to the prototype, CRBs are used, which are resistant to cadmium ions, aluminum foil is added to the medium, cultivation is carried out at a temperature of 28 ° C for 18 days.

The cultivation is carried out in a synthetic medium (table 1 - the composition of the synthetic medium) with the introduction of nutrients that stimulate the growth of bacteria. Nutrients and divalent cadmium are added to the synthetic medium before sowing the bacterial culture. The composition of nutrients and the sequence of their introduction are shown in Table 2. All nutrients, except vitamins, are autoclaved at 1 atm for 30 minutes. The vitamins are sterilized by filtration using a bacterial filter (0.20 μm).

Sowing is carried out in sterile containers with embedded foil, the volume of inoculum (culture of CRP) in the amount of 10% of the volume of the container. The containers with the inoculum are filled with synthetic medium (with all the added nutrients) to the top. The pH of the medium is adjusted to 7.0-7.8 with a NaHCO 3 solution. The vials are closed with aluminum caps, sealed and placed in a thermostat at 28 ° C. The formation of crystals of cadmium sulfide occurs on the foil and partially on the bottom of the bottle. After cultivation, the precipitate is collected from the foil and centrifuged from the bottom of the vial and dried in air. Examples of implementation of the invention in laboratory conditions are given below.

A pure culture of CRP Desulfovibrio sp. A2 was cultured on a synthetic medium containing bivalent cadmium at a concentration of 150 mg Cd / L and aluminum foil. Crystals of cadmium sulfide were obtained on foil and partially at the bottom of a 120 ml bottle. The aluminum foil vials were dry heat sterilized in a 160 ° C sterilizer for 2.2 hours.

Sowing was carried out in a sterile laminar flow cabinet, which was previously disinfected with ultraviolet light for 30 minutes. Before inoculation, the synthetic medium (Table 1) was brought to a boil and then rapidly cooled under running cold water to remove dissolved oxygen. In the medium cooled to room temperature, nutrients were added (table 2) (per 1 l) in the following sequence: vitamins (2 ml), salt solution (10 ml), cofactor solution (1 ml), organic substrate - lactate (1 , 6 ml), NaHCO 3 solution (pH was adjusted to 7.0-7.8), sodium sulfide solution (2 ml). A stock solution of cadmium (CdCl 2 × 2.5H 2 O 2 g per 100 ml of water) was added in an amount of 16.72 ml per 1 liter of synthetic medium (thus, the concentration of cadmium in the medium was 150 mg / l).

About 50 ml of synthetic medium with added additives and 10 ml of inoculum (bacterial culture) were introduced into vials with foil, after which the medium was added to the top. Rubber stoppers were rubbed to the edges of the vials using a sterile needle, which reduced the likelihood of air oxygen penetration. At the end of inoculation, the vials were closed with aluminum caps, the vial was sealed with a sealer, and the thermostat was placed at 28 ° C. Crystallization of cadmium sulfide begins after 10 days of cultivation; upon cultivation for 18 days, cadmium sulfide crystallizes completely. The formed precipitate was collected from the foil and centrifuged from the bottom of the vial and dried in air. The mass of the sediment formed is 0.38 g.

The study of the formed sediments was carried out using scanning electron microscopy (Philips SEM515 with an EDAX ECON IV analyzer). The crystalline phase was determined by X-ray phase analysis on a Shimadzu XRD 6000 diffractometer.

The size of the crystals, determined under a scanning electron microscope, was 50-300 μm, Figure 1 - micrographs (SEM) of sediments obtained during the cultivation of Desulfovibrio sp. A2 in the presence of Cd ions (150 mg / l) for 18 days, and the corresponding emf. The sediments obtained during the cultivation of the strain Desulfovibrio sp. A2 contained cadmium, sulfur, iron, oxygen, carbon, and sodium, with the carbon and oxygen originating from the carbon support on which the sample lay. The ratio of elements is presented in Table 3 - the elemental composition of sediments obtained during the cultivation of Desulfovibrio sp. A2 in the presence of Cd ions (150 mg / L) for 18 days (elements C and O originate from the substrate on which the sample was placed).

When studying the sediments using X-ray phase analysis, the formation of crystalline cadmium sulfide within 18 days was shown (Figure 2 - diffractogram of sediments obtained by cultivating Desulfovibrio sp. A2 in the presence of an initial concentration of Cd (150 mg / L) for 18 days. : CdS - cadmium sulfide).

In the control sediments obtained by incubation without adding inoculum, no crystalline phase was observed and the main elements were cadmium and oxygen. The proposed method includes the possibility of using wastewater and liquid waste from mining and processing metallurgical enterprises as a synthetic medium for producing cadmium sulfide.

CLAIM

A method for obtaining crystalline cadmium sulfide by placing sulfate-reducing bacteria in a synthetic medium containing metals, with the addition of nutrients, including solutions of vitamins, salts, cofactors, characterized in that the sulfate-reducing bacteria Desulfovibrio sp. A2, use a synthetic medium containing a source of cadmium ions - a solution of cadmium chloride, and the concentration of cadmium ions in the synthetic medium is 150 mg / L, while aluminum foil is placed in the cultivation vessel, cultivation is carried out at a temperature of 28 ° C for 18 days, and the sediment collected from the foil and from the bottom of the bottle containing cadmium sulfide crystals is dried.

Sulfides of some other metals (insoluble in water), for example, iron (II), manganese, zinc, do not fall out of an acidic solution, since they are soluble in dilute mineral acids, therefore, not hydrogen sulfide, but ammonium (or sodium) sulfide is used to precipitate them.

FeSO 4 + (NH 4) 2 S \u003d FeS (sediment) + (NH 4) 2 SO 4

Some insoluble sulfides are able to dissolve in an excess of ammonium sulfide or ammonium polysulfide solution (due to the formation of complex salts), while others cannot.

As 2 S 3 (sediment) + 3 (NH 4) 2 S \u003d 2 (NH 4) 3 (solution)

Previously, the property of sulfides to fall out of solution under the action of hydrogen sulfide or ammonium sulfide (as well as dissolve or not dissolve in an excess of solutions of sulfides or polysulfides of monovalent cations) was actively used in analytical chemistry for qualitative analysis and separation of metal mixtures (hydrogen sulfide methods of analysis). Moreover, metal cations in analytical chemistry were classified into groups depending on their behavior when exposed to hydrogen sulfide, ammonium sulfide solution, and polysulfides (of course, this was not the only sign by which cations were classified in analytical chemistry, but one of the main ones).

In our time, hydrogen sulfide methods of analysis have almost lost their relevance, since hydrogen sulfide is poisonous. Moreover, hydrogen sulfide is not only poisonous but also insidious. At first, the characteristic smell of hydrogen sulfide (rotten eggs) is well perceptible even in low concentrations, but with prolonged exposure of the experimenter to hydrogen sulfide, the smell of hydrogen sulfide ceases to be felt. As a result, you can be exposed to dangerous concentrations of hydrogen sulfide without even knowing it. Earlier, when working with hydrogen sulfide was the order of things in laboratory classes in analytical chemistry, this happened often.

Over the years, analytical chemists have been able to come up with a replacement for hydrogen sulfide and sulfides (the so-called non-hydrogen sulfide analysis methods). In addition, physicochemical and instrumental methods of analysis are increasingly used in analytical chemistry.

I decided to get some insoluble sulfides from solutions of metal salts and hydrogen sulfide. The choice fell on copper and cadmium (there was also a thought about mercury, but I refused it, since there was little mercury, and it was in the form of a metal). The experiments were carried out on the street. Working at home with hydrogen sulfide is a kamikaze occupation. This is only permissible with a fume hood.

Took copper sulfate and cadmium acetate (both qualifications "Ch"). Dissolve the salt in warm water. First, copper sulfate was treated with hydrogen sulfide. The vial quickly filled with black flakes of copper sulfide CuS. He left the test tube for a while, walked away (don't forget - hydrogen sulfide is poisonous!). When I arrived, I found in the test tube, instead of liquid, a dark porridge made of solution and sediment.

I rinsed the gas pipe after the copper and proceeded to the cadmium. A yellow film of cadmium sulfide quickly formed on the walls at the top of the liquid. Soon the solution was covered in flakes. I walked away again. Fifteen minutes later he came and found porridge with yellow-orange stains in a test tube. This is cadmium sulfide CdS.

Despite the toxicity of cadmium, cadmium sulfide is still used today as a pigment due to its beautiful color, lightfastness and chemical resistance. Sometimes a solid solution is used between cadmium sulfide and selenide Cd (S, Se): by changing the ratio of selenium and sulfur in the pigment, you can vary its color.

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Cadmium (II) oxide

When heated in air, cadmium ignites, forming cadmium oxide CdO (molecular weight 128.41). The oxide can also be obtained by calcining cadmium nitrate or carbonate salts. In this way, the oxide is obtained in the form of a brown powder, which has two modifications: amorphous and crystalline. When heated, amorphous oxide turns into crystalline, crystallizing in a cubic system: it adsorbs carbon dioxide and behaves like a strong base. The heat of transformation of CdO AMORPHN CdO CRYST is 540 cal.

The density of the artificially prepared oxide ranges from 7.28 to 8.27 g / cm 3. In nature, CdO forms a black plaque on the gum, with a density of 6.15 g / cm 3. Melting point 1385 °.

Cadmium oxide is reduced by hydrogen, carbon and carbon monoxide. Hydrogen begins to reduce CdO at 250-260 ° by a reversible reaction:

CdO + H 2 Cd + H 2 O,

Which ends quickly at 300 °.

Cadmium oxide dissolves well in acids and in a solution of zinc sulfate by a reversible reaction:

CdO + H 2 O + ZnSO 4 CdSO 4 + Zn (OH) 2.

Cadmium sulfide

Sulfide (CdS, molecular weight 144.7) is one of the important cadmium compounds. It dissolves in concentrated solutions of hydrochloric and nitric acids, in boiling dilute sulfuric acid and in solutions of ferric iron; in the cold, it dissolves poorly in acids and is insoluble in dilute sulfuric acid. The product of sulfide solubility is 1.4 · 10 -28. Crystalline sulfide occurs naturally in the form of grenakite as an impurity to heavy and non-ferrous metal ores. It can be artificially obtained by fusing sulfur with cadmium or with cadmium oxide. When metal cadmium is fused with sulfur, the development of the sulfide formation reaction is inhibited by protective films of CdS. Reaction

2CdO + 3S \u003d 2CdS + SO 2

begins at 283 ° and at 424 ° passes at high speed.

Three modifications of CdS are known: amorphous (yellow) and two crystalline (red and yellow). The red variety of crystalline sulfide is heavier (specific gravity 4.5) than yellow (specific gravity 3). Amorphous CdS becomes crystalline when heated to 450 ° C.

When heated in an oxidizing atmosphere, cadmium sulfide is oxidized to sulfate or oxide, depending on the firing temperature.

Cadmium sulfate

Cadmium sulfate (CdSO 4, molecular weight 208.47) is a white crystalline powder that crystallizes in the rhombic system. It is readily soluble in water but insoluble in alcohol. Sulfate crystallizes from an aqueous solution in a monoclinic system with 8/3 water molecules (CdSO 4 8 / 3H 2 O), is stable up to 74 °, but at more high temperature turns into monohydric sulfate (CdSO 4 H 2 O). With increasing temperature, the solubility of sulfate slightly increases, but with a further increase in temperature it decreases as shown in table 3:

Table 3

The existence of three sulfate modifications was established: b, c and d. After the isolation of the last water molecule at 200 ° from the crystalline hydrate 3CdSO 4 · 8H 2 O, the b-modification is formed, which is stable up to 500 °; with a further increase in temperature, the s-modification arises, which at temperatures above 735 ° passes into the r-modification. High-temperature modifications (c and d) on cooling pass into b-modification.

Introduction

Currently, the number of materials used in electronic engineering for various purposes is several thousand. According to the most general classification, they are divided into four classes: conductors, semiconductors, dielectrics and magnetic materials. Among the most important and relatively new materials are semiconductor chemical compounds, among which compounds of the type A II B VI are of the greatest scientific and practical interest. One of the most significant materials in this group is CdS.

CdS is the main modern infrared technology, since its photosensitivity spectrum overlaps the atmospheric transparency window (8-14 microns), in which all objects of the environment emit. This allows it to be used in military affairs, ecology, medicine and other branches of human activity. To date, CdS is obtained in film form by the hydrochemical method.

The purpose of this course project is to implement a project for the production of sensitive elements of photoresistors based on CdS by the hydrochemical method with a capacity of 100 thousand pieces / year, as well as familiarization with the calculation method designed to preliminary determine the conditions for the formation of CdS, hydroxide and cadmium cyanamide.

Characterization of cadmium sulfide

The diagram of the Cd - S system is not built, the system has one CdS compound existing in two modifications: b (hexagonal) and c (cubic). CdS occurs naturally as the minerals greenockite and howliite.

Crystal structure

Compounds of the A II B VI type usually crystallize in the structure of sphalerite or wurtzite. The sphalerite structure is cubic, type B-3, space group F4 3m (T d 2). The structure of wurtzite is hexagonal, type B-4, space group P 6 3 mc (C 6v 4). These structures are very similar to each other, they have the same number of atoms in both the first and the second coordination sphere - 4 and 12, respectively. The interatomic bonds in the tetrahedra of both modifications are very close.

Cadmium sulfide was obtained with both sphalerite and wurtzite structures.

Thermodynamic and electrophysical properties

Cadmium sulfide is a one-sided phase of variable composition, always having an excess of cadmium. Cadmium sulfide when heated to 1350 ° C sublimates at atmospheric pressurewithout melting, in a vacuum at 180 ° C, it is distilled, without melting and without decomposition, under a pressure of 100 atm, it melts at a temperature of about 1750 ° C. The degree of dissociation of cadmium at temperatures above 1000 ° C reaches 85-98%. Heat of formation of CdS D H 298 0 \u003d -34.71 kcal / mol.

The properties of CdS can be different depending on the conditions of production and heat treatment. Thus, crystals grown in an excess of cadmium vapors have significantly higher thermal conductivity than crystals grown under conditions of stoichiometric composition. The resistivity of CdS, depending on various factors, can vary over a wide range (from 10 12 to 10 -3 ohm * m).

Deviations from stoichiometry have a decisive influence on the electrophysical properties of CdS. The introduction of oxygen into the samples leads to a strong decrease in electrical conductivity. The band gap of CdS, determined from optical data, is 2.4 V. Cadmium sulfide usually has n-type conductivity, which is due to the lack of sulfur in relation to the stoichiometric composition.

The solubility of cadmium in water is insignificant: 1.5 * 10 -10 mol / l.