CZ303308B6 - Method of removing thallium, optionally thallium and cadmium from contaminated water using zinc - Google Patents

Abstract

The invented method of removing thallium, optionally thallium and cadmium from contaminated water using zinc is characterized in that contaminated water containing thallium cations, optionally cations of thallium and cations of cadmium at a concentration of 1 to 1000 mg/l is treated with zinc at a temperature ranging from 5 to 35 degC for a period of 0.1 to 10 hours.

Description

Method for removing thallium, possibly thallium and cadmium, from contaminated water with zinc

Technical field

The invention relates to a process for the removal of thallium, optionally thallium and cadmium, from contaminated water with zinc, which comprises reducing thallium cations and optionally also cadmium cations to their metallic forms.

BACKGROUND OF THE INVENTION

Thallium and cadmium are heavy metals whose compounds are highly toxic. Thallium is potentially carcinogenic, cadmium is a proven carcinogen. Their release into the t5 environment is therefore very undesirable.

Thallium enters the environment mainly in the treatment of sulphide ores of copper, lead and zinc, which contain thallium as an additive, and in the recycling of products made of these metals. Thallium contamination of the environment occurs to a lesser extent when it is used in industrial production - special types or glass or photocells.

The source of cadmium emissions into water is waste water from galvanic plating and from production of Ni-Cd accumulators and batteries. Phosphate fertilizers and sewage sludge are important anthropogenic sources of cadmium,

In waters cadmium occurs as a single ion, a hydroxocomplex, a carbonatocomplex and optionally a sulphatocomplex. The organic complexes are mainly complexes with humic substances. The dominant form of cadmium is Cd ²⁺ .

Thallium occurs almost unpolluted in unpolluted waters. Increased concentrations are caused by human intervention.

The separation of thallium from solution is directed to patent CZ 300444, which is concerned with the removal of thallium ions from a solution of aluminum salts on ion exchangers containing thiol or thiouront functional groups or their derivatives. A disadvantage of this method of separating thallium from solution is its use only in the acidic region in the presence of specific compounds.

Another Czech patent CZ 300285 discloses a method for removing thallium from ammonium alum. To do this, oxidation of Tf to Tl ³⁺ using ammonium persulfate is utilized, Tl ³⁺ no longer enters the alcove lattice grid 40 and remains in the reaction mixture (solution). This method solves the preparation of thallium-free alum and does not solve the separation of thallium from the aqueous medium.

Spanish patent ES 2116787 describes the precipitation of thallium in solution with a suitable sulfide solution. Thallium can be selectively separated from other metals in this manner to give the corresponding thallium sulfide.

Patent CN 101337731 is concerned with the removal of cadmium from industrial wastewater by means of a biological absorbent, which is a rdest plant. These aquatic plants very effectively separate cadmium from industrial wastewater and are subsequently burned.

Another patent, CN 101264966, describes the use of waste beer yeast for the removal of cadmium ions from waste water as a highly effective separation method.

A disadvantage of patents for the separation of cadmium from wastewater using biological active substances is their limited applicability.

- 1 GB 303308 Β6

One method of separation of cadmium from solution is by adsorption on suitable sorbents, e.g. according to patent CN 1884120, sorbent hydrated MnO ₂ and according to patent CN 1817441 it is a sorbent prepared from activated carbon and MnO ₂ . The disadvantage of these is the use of MnO ₂ .

The above drawbacks at least partially eliminate the process of removing thallium, optionally thallium and cadmium, from contaminated water with the zinc of the invention, which makes it possible to remove thallium or thallium together with cadmium from the contaminated water to form further workable insoluble mixtures of these metals and their compounds.

SUMMARY OF THE INVENTION

A method for removing thallium, optionally thallium and cadmium, from contaminated water with zinc is to treat contaminated water containing thallium cations at a concentration of 1 to 1000 mg / l with zinc at a temperature of 5 to 35 ° C for 0.1 to 10 hours .

A preferred method of removing thallium, optionally thallium and cadmium, from contaminated water with zinc is to do so. by treating contaminated water containing thallium cations and cadmium cations at a concentration of 1 to 1000 mg / l.

Another preferred method of removing thallium, optionally thallium and cadmium, from zinc contaminated water is to add 1000 parts by weight of contaminated water to the batch stirred tank reactor and to add 0.1 to 20 parts by weight of zinc having a particle size of 20 to 60 µm and then the reaction mixture is stirred for 0.1 to 10 hours.

Another preferred method of removing thallium, optionally thallium and cadmium, from zinc contaminated water is that the contaminated water flows through a flow reactor with a zinc layer having a particle size of up to 0.5 to 50 mm at a rate of 0.5 to 20 m / day.

Speed (m / day) means the volumetric flow (m ³ / day) related to the internal cross-section of the flow reactor (m ² ) perpendicular to the flow direction. The volume flow density (m / day) is also used for the velocity defined in this way.

When removing thallium or thallium together with cadmium from contaminated zinc water, the thallium, optionally thallium cations and cadmium cations in the reaction mixture are reduced to metals which react with water to form an insoluble mixture of the compounds of these metals. Unreacted thallium, thallium and cadmium residues also remain in the resulting insoluble mixture. At the same time, zinc oxidizes and passes into solution in the form of Zn ²⁺ cations. The resulting insoluble mixture of thallium, optionally thallium and cadmium and their compounds is then filtered off.

In the flow-through method for the removal of thallium, respectively thallium and cadmium, from contaminated zinc water, chemical reactions take place continuously until the thallium or thallium and cadmium concentrations in the effluent from the flow reactor are increased above the limit concentration. Contaminated water containing thallium cations or thallium cations and cadmium cations is fed to a zinc-filled reactor bed layer in which thallium or thallium cations and cadmium cations are reduced to metals and reacted with water to form an insoluble mixture of the metal and its compounds. unreacted residues. The resulting insoluble mixture is separated in the interstitial space of the reactor packing (the space between the grains of the reactor packing). Water with reduced thallium, eventually thallium and cadmium concentrations flows out of the flow reactor. The effluent decontaminated water contains, depending on the pH, a variable amount of zinc in the form of Zn - cations. In this method of separating thallium, respectively thallium and cadmium, the volume and shape of the flow reactor charge are variable, which are determined according to the amount of contaminated water to be treated, the input concentration of thallium and thallium and cadmium respectively, the volumetric flow density and the residence time of the contaminated water. flow reactor.

-2GB 303308 B6

Zinc reducing abilities are also highly dependent on its specific surface area. Powdered zinc having a particle size of 20 to 60 µm is used for the batch arrangement. Granular zinc, lump and the like with a particle size of 0.5 to 50 mm are used for the flow arrangement.

The chemical reactions taking place in these processes can be represented by the following equations:

ΤΓ + Zn '-> 2 ° + Ζη ² ' (1)

Cd ^2r + Zn ° -> Cd ° + Zrv '(1)

The advantages of the method of removing thallium, optionally thallium and cadmium, from the contaminated water with zinc according to the invention are:

- removal of highly toxic metals from contaminated water;

- high efficiency even at low doses of zinc;

a technologically easy method of removing thallium, optionally thallium and cadmium, from contaminated water;

the product is an insoluble mixture of reduced thallium, optionally thallium and cadmium metals and their compounds;

the resulting insoluble mixture of reduced thallium, optionally thallium and cadmium and their compounds may be used to obtain pure thallium, optionally thallium and cadmium and their compounds;

economical way of separation,

DETAILED DESCRIPTION OF THE INVENTION

Example 1

The model experiment was conducted in a 150 cm ³ flow reactor, placed in a 20 ° C tempered pool to ensure isothermal activity. The flow reactor was filled with granulated 5 to 10 mm zinc weighing 636 g. A 20 mg / l thallium model solution was used in the experiment. The volumetric flow rate was 0.5 cmVmin, and this volumetric flow rate corresponded to a volumetric flow density of 1.2 m / day and a residence time in the cartridge of about 4 hours.

After 199 days, 152 liters of the model solution were treated corresponding to a volume flow rate of 0.53 cm ³ / min. The thallium concentration at the outlet of the through-flow reactor was below the detection limit, ie, below 0.1 mg / L. Thallium separation efficiency exceeded 99%.

Example 2

The quarter-trial experiment was conducted in a flow reactor of 1 dm ³ , located in a 20 ° C tempered pool to ensure isothermal performance. The reactor charge consisted of granulated zinc of 5 to 15 mm in size, weighing about 2 kg. The volumetric flow rate of contaminated water through the flow reactor was chosen at 5 cm ³ / min. This volumetric flow rate corresponded to a volumetric flow density of 0.9 m / day and a residence time in the reactor of 1.5 hours. Contaminated water can be characterized as a chloride-sulphate system with a high alkali content (cNa ⁼ 8 g / l, cK = 5 g / l), pH - 8 to 9 and a high concentration of monitored contaminants, ie 30 mg / l thallium and 60 mg / l. 1 cadmium. 421 liters of contaminated water were processed in 59 days, which corresponded

The actual flow rate of contaminated water is 5.5 cmVmin., Ie about 7.9 l / day. The separation efficiency of both thallium and cadmium from contaminated water was higher than 99%.

Table 1 shows the contents of thallium, cadmium and zinc at the inlet and outlet of the flow reactor:

Table 1

Time duration process Thallium and cadmium separation Chemical composition of incoming contaminated water Chemical composition of output decontaminated water Zn-input Tl-input Cd-input Zn-output Tl-output Cd-output [day] [mg / 1] [mg / 1] [mg / 1] [mg / 1] [mg / 1] [mg / 1] 0 0.15 34.5 62.6 31.2 <1 <1 4 0.15 34.5 62.6 31.2 <1 <1 11 0.15 20.4 64.5 40.7 <1 <1 18 0.15 35.2 63.4 45.0 <1 <1 25 0.19 26.7 67.1 44.9 <1 <1 32 0.24 27.5 59.5 48.4 <1 <1 39 0.25 30.1 65.5 50.2 <1 <1 46 0.25 29.8 63.6 49.7 <1 <1 53 0.19 29.8 63.6 46.5 <1 <I

Example 3

The pilot plant experiment was conducted in a two-stage flow reactor with a volume of 2x40 dm ³ . The pilot plant consisted of a preparatory and technological node. In the preparatory node of the apparatus there was a mechanical pre-treatment of waste water consisting of filtration of waste water on a sand filter. In the technological node of the apparatus there was a two-stage separation of thallium and cadmium by zinc reduction, followed by adsorption of zinc ions released in the process.

The reactor charge consisted of lump zinc of 5 to 20 mm and weighing 360 kg. The contaminated water flow through the reactor was provided by a peristaltic metering pump and was selected at 50dm ³ / h. This volumetric flow rate corresponded to a volumetric flow density of 14 m / day and a residence time in the reactor of 0.44 hours.

Contaminated water can be characterized as a chloride-sulphate system with a high content of dissolved inorganic salts (at the solubility limit), pH = 8 to 9.5 and a high concentration of monitored contaminants, ie 30 to 130 mg / l thallium, average value 67 mg / l thallium , and 40 to 140 mg / l cadmium, an average value of 64 mg / l cadmium.

At the output of the 2nd reaction stage of the flow reduction reactor, the thallium concentration values ranged from 1 to 2 mg / l and the cadmium concentration values ranged from 2 to 3 mg / l, corresponding to a thallium separation efficiency of greater than 97% and a cadmium separation efficiency of approx. 96%.

-4GB 303308 B6

Example 4

A 100 ml batch reactor was charged with 100 ml of distilled water and weighed 0.5 g of zinc powder with an average particle size of 40 µm. The resulting reaction suspension was stirred for 30 minutes. Agitation of the reaction slurry was provided by the stirrers of separate electromagnetic stirrers. Subsequently, 331.2 ml of distilled water and 178.8 ml of thallium acetate model solution were added. The initial thallium concentration in the reaction mixture was 300 mg / L. The temperature of the reaction mixture was kept constant at 20 ° C by placing the reactors 10 in a tempered pool flowing through the tempering water of the external circuit from the thermostat. The reaction time was 2 hours. The resulting reaction slurry was then filtered through a glass microfibre filter membrane. The output thallium concentration was 0.4 mg / L. The separation efficiency of thallium from solution was 99.9%.

Example 5

A 100 ml batch reactor was charged with 100 ml of distilled water and weighed 0.5 g of zinc powder with an average particle size of 40 µm. The resulting reaction slurry was stirred for 30 minutes. Agitation of the reaction slurry was provided by the stirrers of separate electromagnetic stirrers. Subsequently, 400 ml of a 1000 mg / l thallous acetate model solution was added. The temperature of the reaction mixture was kept constant at 20 ° C by placing the reactors in a tempered pool flowing through the tempering water of the external circuit from the thermostat. The reaction time was 2 hours. The resulting reaction slurry was filtered through a glass microfiber filter membrane. The output thallium concentration was 0.7 mg / L. The separation efficiency of thallium from the solution was 99.3%.

Example 6

A 600 ml batch reactor was charged with 500 ml of an aqueous solution of the following composition:

element CD Fe Mg Pb Tl Zn concentration [mg / 1] 72.5 0.2 19.1 2 28.6 1.3

0.2 g of zinc powder with an average particle size of 40 µm was then added. The resulting reaction suspension was stirred for 180 minutes. Agitation of the reaction slurry was provided by the stirrers of separate electromagnetic stirrers. The temperature of the reaction mixture was kept constant at 20 ° C so. that the reactors were placed in a tempered pool flowing through the temp. The resulting reaction slurry was then filtered through a glass microfibre filter membrane. The output thallium concentration was 0.3 mg / L. The efficiency of thallium separation from the solution was 99.0%.

Example 7

A 100 ml batch reactor was charged with 100 ml of distilled water and weighed 10 g of dendritic zinc having a size of 1 to 4 mm and the composition:

-5GB 303308 B6

element Si WITH Cl TO Ca Fe Zn Sn TI Pb concentration% wt. 0.35 0.1 0.14 0.06 0.06 0.03 91.2 0.01 0.02 8

The resulting reaction suspension was stirred for 30 minutes. Agitation of the reaction slurry was provided by the stirrers of separate electromagnetic stirrers. Subsequently, 396.6 ml of distilled water and 3.4 ml of a 1000 mg / l thallous acetate model solution were added. The initial thallium concentration was 100 mg / l. The temperature of the reaction mixture was kept constant at 20 ° C by placing the reactors in a tempered pool flowing through the tempering water of the external circuit from the thermostat. The reaction time was 2 hours. The resulting reaction slurry was then filtered through a glass microfibre filter membrane. The output thallium concentration was 0.9 mg / L. The efficiency of thallium separation from the solution was 99.1%.

Industrial applicability

The process for removing thallium, optionally thallium and cadmium, from contaminated water with zinc is industrially applicable in the purification of waters containing dissolved salts of thallium, optionally thallium and cadmium.

Claims (4)

PATENT CLAIMS Method for removing thallium, optionally thallium and cadmium, from contaminated water with zinc, characterized in that contaminated water containing thallium cations of a concentration of 1 to 1000 mg / l is treated with zinc at a temperature of 5 to 35 ° C for 0.1 up to 10 hours. 2. The removal method of claim 1, wherein the contaminated water comprises thallium cations and cadmium cations at a concentration of 1 to 1000 mg / l. Removal process according to claim 1 or 2, characterized in that 1000 parts by weight of contaminated water are introduced into the batch stirred tank reactor and 0.1 to 20 parts by weight of zinc having a particle size of 20 to 60 μπι are introduced and the reaction mixture is stirred for 0.1 to 10 hours. Removal process according to claim 1 or 2, characterized in that the contaminated water flows through a through-flow reactor with a zinc layer having a particle size of up to 0.5 to 50 mm at a speed of 0.5 to 20 m / day.