FI59972B - FOERFARANDE FOER RENING AV SVAVEL FRAON ARSENIK - Google Patents

Description

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Patmt- och registervtyrulMn '' AmMcu uchgd och utUkrifun puMiund 31.07.8l (32) (33) (31) Requested «uoIImui — H« gird prlorttut (71) Gosudarstvenny Nauchno-Issledovatelsky Institut Tsvetnykh Metallov, ulit SU) (72) Igor Mikhailovich Nelen, Moscow, Vladimir Ivanovich Goryachkin,

This invention relates to a process for obtaining elemental sulfur free of arsenic mixtures from sulfur-containing materials.

Elemental sulfur is used in the production of sulfuric acid, in the rubber, pulp and paper industries, in organic synthesis (for the production of sulfur dyes and carbon sulphides, vulcanisation accelerators and pharmaceuticals) and in agriculture. The presence of arsenic, which is characteristic of gaseous sulfur in particular, causes difficulties in its use.

Methods based on the use of calcium oxide or calcium hydroxide to purify sulfur from arsenic are known in the art.

Thus, for example, a sulfur purification method is known in which molten sulfur is treated in an autoclave with lime milk to wash arsenic.

The disadvantages of the known methods are that it is necessary to treat the arsenic-containing waste liquors (or to purify them for reduction), in which case a relatively complex apparatus is required to do this, since the process takes place under pressure.

The object of the present invention is to eliminate the above-mentioned drawbacks.

According to the method known from DE-A-576 251, arsenic is removed from molten sulfur by adding an alkali metal or alkaline earth metal oxide, hydroxide, carbonate or sulphide or a mixture thereof, for example calcium hydroxide or sulphide and sodium hydroxide or sulphide as a suspension or concentrated solution.

Depending on the reagent used for the purification of sulfur, the impurities are obtained either in the form of a salt or in the form of a solution, i.e. in such a form that further treatment is required in order for arsenic to be exploited or excavated.

It is known from GB patent 733 6oU to purify sulfur from arsenic by means of a fine powder such as calcium hydroxide or barium hydroxide or a mixture thereof and sodium carbonate or bicarbonate by passing water vapor through the reactor. The impurities then precipitate with the product formed as a fine paste within one hour.

The present invention differs from the known methods of DE-576 251 and GB-733 Sok in that the removal of arsenic by means of an alkaline earth metal oxide or hydroxide is carried out in the presence of a new reagent which is an aqueous solution of an inorganic salt and has a higher boiling point than sulfur. whose anion forms a compound soluble with calcium.

It is therefore a particular object of the present invention to modify the process conditions associated with a process for purifying sulfur from arsenic by treating molten sulfur with calcium oxide or calcium hydroxide.

The object of the present invention is achieved by treating molten sulfur in the presence of an aqueous solution of alkali or alkaline earth metal salts having a boiling point higher than the melting point of sulfur and whose anions form soluble compounds with calcium.

Aqueous solutions of potassium, sodium, calcium, magnesium, barium and ammonium chlorides or nitrates or mixtures thereof are used as aqueous solutions of inorganic salts, as these are the most readily available substances.

The use of an aqueous solution of these compounds is based on the fact that for the reaction between the arsenic compounds and the lime, the dissolution of the lime is necessary to ensure the purification of the sulfur. These compounds do not react directly in molten sulfur.

The formation of insoluble compounds between the anion and calcium of the solution is undesirable because lime, as mentioned above, reacts with the arsenic compounds in the dissolved state.

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When such an aqueous solution of inorganic salts is added to molten sulfur, it is dispersed inside the sulfur as droplets. The solid components of the treated melt, i.e. the excess lime, the compounds formed in the reaction, including the arsenic-containing compounds and the ash mixtures of the original sulfur, get better wetted from said aqueous solution than molten sulfur and thus accumulate inside the droplets of said solution due to surface tension forces.

When treating molten sulfur in the presence of a suitable amount of an aqueous solution having a boiling point higher than the melting point of sulfur, the arsenic (3) compounds can be isolated as granular arsenic-containing lumps or pulp.

In order to obtain a solid, hard, spherical granular arsenic-containing cake or briquette, it is preferred that the molten sulfur be treated in the presence of 1-15 liters of an aqueous solution of inorganic salts having a boiling point higher than the melting point of molten sulfur. for.

The process for purifying sulfur from arsenic according to the invention offers the following advantages: (1) The formation of arsenic-containing solutions is prevented (by isolating arsenic as granular or pasty lump); (2) Arsenic is isolated as a single dust-free product (arsenic cake) that is easy to transport and bury; (3) The method is carried out using a conventional (non-autoclave) apparatus because the treatment of molten sulfur is carried out in the presence of an aqueous solution having a boiling point higher than the melting point of sulfur.

When sulfur purification is carried out according to the invention by forming an arsenic cake, this cake is the only by-product. All of the arsenic isolated from the sulfur is concentrated in the cake. The aqueous solution present in molten sulfur during processing is contained in the cake thus formed.

The sulfur purification process according to the invention for removing arsenic is carried out as follows.

A vessel equipped with a stirrer is charged with molten sulfur to be cleaned. Lime and an aqueous solution of inorganic salts are also added to this vessel. As the aqueous solution of inorganic salts, for example, aqueous solutions of nitrites, nitrates, chlorides, bromides, iodides, permanganates, formates, thiosulfates and acetates can be used. Lime can be added to molten sulfur as either dry lime oxide or calcium hydroxide (either before or after feeding an aqueous solution of inorganic salts to the melt). In addition, the lime can be fed as molten lime milk prepared, for example, in said aqueous solution. The process is advantageous with vigorous stirring and that the temperature of the bath does not exceed 160 ° C (because above this temperature the viscosity of the sulfur increases strongly), and is preferably U -120 ° C.

An aqueous solution of inorganic salts can be added to the molten sulfur at the required concentration, i.e., the boiling point of the solution is higher than the melting point of the sulfur. The temperature conditions recommended for sulfur treatment depend on the concentration of the solutions. Thus, for example, when an aqueous solution of calcium chloride is used, the salt concentration and the boiling point of the solution relative to each other are as shown in the following table.

Table

Concentration,% Boiling point, ° C

3U, 5 llU

UO 119 hl 120 * + 5.8 125 50.8 130 57.9 1U0

It is preferred that the purification process be carried out under conditions which ensure the formation of the arsenic-containing substance into solid granules (the latter being easier to transport and dig into the ground or being most suitable for further treatment). For this purpose, the amount of solution having a boiling point higher than the melting point of sulfur and used to treat molten sulfur should be 1 to 15 liters per kilogram of arsenic contained in the sulfur to be purified. The size of the granules can be easily adjusted to a range of 0.5 to 25 mm by using efficient mixing, suitable dosing of the aqueous solution, adjustment of the process temperature and its duration. The reaction between lime and the arsenic compounds in the sulfur to be purified and the precipitation of arsenic as solid granules takes 2-1 + 0 minutes, depending on the conditions used in the process. After the formation of granules, it is preferable to raise the temperature of the bath from 11 * -120 ° C (melt sulfur treatment temperature) to 130-150 ° C. This causes additional hardening of the formed granules due to partial evaporation of the aqueous solution and reduction of sulfur viscosity. later subsequent separation of the granules and reducing the sulfur losses in this context. The arsenic separated from the sulfur is concentrated in the granules, and arsenic is, as previously shown, a uniform, dust-free product that is easy to transport or dig into the ground or also easy to further process. The molten sulfur is separated from the arsenic-containing cake by conventional methods such as filtration or centrifugation.

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To regenerate the inorganic salts, the granules can be washed with water and the resulting solution can be recirculated to the first step of the process, or an aqueous starting solution of the inorganic salts can be prepared therefrom.

If the amount of aqueous solution of inorganic salts for treating molten sulfur exceeds 15 liters of solution per kilogram of arsenic above, the arsenic-containing compounds differ from the sulfur to be purified in the form of a pasty arsenic-containing cake or mass, which is more complicated than purified sulfur.

The present invention will be more readily understood from the following examples in which sulfur is purified from arsenic.

Example 1 600 g of gaseous sulfur are melted in a steel cylinder with sulfur containing 0.6% by weight of arsenic. At 11 ° C, 11 g of dry calcium oxide are fed to the melt. After maintaining the mixture at this temperature for 30 minutes and stirring continuously, 25 ml of 39% aqueous calcium chloride solution are added thereto, the solution having a boiling point of 18 ° C. The contents of the cylinder are then kept at 11 ° C for one hour and then heated to 130 ° C and filtered through glass wool in a vacuum filter heated to the same temperature. Purified sulfur separates from arsenic granules. The arsenic content in the filtered sulfur is 0.0002 wt. The arsenic cake has a granule size of 2-10 mm and a sulfur content of 18.0% by weight and an arsenic content of 6.5% by weight. When the granules are washed to regenerate calcium chloride, 3.5% by weight of the arsenic in the granules enters the aqueous extract.

Example 2 To 600 g of molten sulfur containing 0.6% by weight of arsenic, lime milk is added with stirring at 18 ° C, this lime milk being prepared from 13.5 g of calcium oxide and 30 ml of 39% calcium chloride. aqueous solution. After maintaining the mixture at said temperature for 20 minutes, the contents of the bath are heated to 135 ° C and then filtered. The purified sulfur is separated from the granules of the arsenic-containing cake. The filtered sulfur contains 0.0001 wt.% Of arsenic, with a sulfur yield of 97.8 wt.% Of charged sulfur. The size of the arsenic cake granules is U-8 mm with a yield of 10, U by weight of # charged sulfur.

Example 3

Molten sulfur (600 g) containing 0.6% by weight of arsenic is fed with stirring at 132 ° C 22 ml of a 32% strength by weight aqueous solution of calcium chloride (the boiling point of the solution is 112 ° C); the bath temperature is lowered to 11 ° C. 13.5 g of calcium oxide are then added and the bath is kept under stirring at this temperature for minuutin0 minutes, after which the 6 59972 bath is heated to 130 ° C and filtered. The purified sulfur is separated from the granules of the arsenic-containing cake. The arsenic content of the sulfur thus obtained is 0.002% by weight.

Example U

A bath equipped with stirrers is fed with 18.8 tons of molten sulfur containing 0.6 wt.% Of arsenic, 0.2 wt.% Of ash and a degree of acidity of 0, OUU #. At a temperature of 113 ° C, the bath is fed with calcium hydroxide per 21.1 kg of sulfur. The contents of the bath are stirred for five minutes until a homogeneous mass is obtained and then poured into i * 0% by weight aqueous calcium chloride solution at a rate of 29.7 liters per tonne of sulfur (the boiling point of the solution is 119 ° C). After the bath is kept for half an hour to 113 ° C and is continuously stirred, purified sulfur is separated from the arsenic cake clumped average pakoislingolla.

Purified sulfur contains 0.002% by weight of arsenic and has an ash content of 0.0k # and an acidity of 0.0011 #. The sulfur yield is 98.2% by weight of # pressed sulfur. The yield of granules of the arsenic-containing cake is 9.1% by weight of the charged sulfur with a grain size of U-7 mm and an arsenic content of 6.6% by weight.

Examples 5 ~ 16

13.5 g of dry calcium chloride are fed to molten sulfur (600 g) containing 0.6% by weight of arsenic. The aqueous solution of the inorganic salts is added in two portions with an interval of 30 to 10 minutes between portions and a melt temperature of 11-117 ° C. After the second batch, the melt temperature is raised to 120-125 ° C. The total duration of the sulfur treatment from the beginning of the first aqueous solution feed is 60 minutes. The purified sulfur is separated from the arsenic cake by filtration.

The results obtained are shown in the following table.

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Table

Eg Salts Used Feed Arsenic No. Aqueous Solution Volume, ml Concentration

Salt Saline Solution First- Second Purified Sulfur Concentration Boiling Feed- Feed. * weight- #point / ° C input charge Pain ° ° 5 MgCl2 33 120 10 25 0.006 6 MgCl2 29.8 120 20 25 0.02 KCl 2.7 7 NH ^ Cl n. i + 5 115 20 l8 0.0¾ 8 Ca (NO3) 2 60 120 19 1¾ 0.001 9 Mg (NO3) 2 n. U5 120 19 l6 0.003 10 KN03 75 115 25 25 0.0008 11 NaU03 68 120 25 25 0.0012 12 NHj ^ KO 70 120 15 10 0.01¾ 13 KJ 65 116 20 22 0.008 1¾ NaBr 5¾ 115 120 25 0.01¾ 15 Na2S2 ° 3 70 122 15 25 0.02 16 NaCl2H3 ° 2 67 125 18 15 0.03