CS218929B1 - A method for the treatment of acid wastewater arising from the extraction, treatment and processing of mineral resources and chemical production - Google Patents

Abstract

The invention relates to a method for purifying waste acidic waters that arise during the extraction, chemical treatment and processing of mineral raw materials (for example, purifying mine waters from surface brown coal mines), which contain cations of divalent or trivalent metals containing iron ions and sulfate anions. These waters are first neutralized with limestone or dolomite. Before neutralization, additional iron ions or cations of other divalent metals, preferably magnesium, can be added to the solution in order to achieve the stoichiometric ratio required for the formation of ferrites. After separation of the pure water, the remaining suspension of the solid insoluble neutralization product is oxidized at an elevated temperature of 40 to 100 °C with oxygen and then separated from the clarified water in the form of a granular precipitate. Before heating, it is possible to reduce the volume of the suspension of the solid insoluble neutralization product by sedimentation in a gravitational or centrifugal field.

Description

BACKGROUND OF THE INVENTION The present invention relates to a process for the purification of acidic acids, in particular from mineral processing and chemical production.

Ρή Mining, treatment, refining, use and processing of raw materials, in particular mineral and chemical production, may be caused by acidic waste water containing also divalent and trivalent metal cations containing 'iron' and anions predominantly of sulphates, arsenates, etc. Acidic water is utilized by neutralization with limestone, lime, barium hydroxide, sodium, caustic and other basic additives, where the dissolved metals fall out of solution as insoluble or sparingly soluble compounds, mainly hydroxides. The anions remain in solution or are bound as sparingly soluble compounds.

The disadvantage of these processes is that the precipitates formed are very bulky and aquifers and therefore difficult to separate from the suspension by sedimentation or filtration. During their storage they gradually leach and there is a danger of penetration into the soil. and vodbteči. Metal hydroxides are 'not' -for ^four current conditions of precipitation techniques separable, both for their size colloidal, sorptive capability and dilution, and secondly for the small difference in their physical 'properties. The advantage of this procedure is in some cases lower costs.

In the production of ferrite, a method of precipitating it from aqueous solutions containing divalent and trivalent metal ions has been developed in recent years. This process produces well-settling and easily filterable precipitates which have excellent magnetic properties and are characterized by almost perfect water insolubility and stability. In particular, alkali alkalis are used to precipitate them from the solutions. The conditions between the type of precipitate and the shape and size of the particles have already been clarified. It has been found that trivalent iron ions coexisting in an appropriate ratio with divalent iron ions, which may be represented by other divalent metal ions in the aqueous solution, react with caustic precipitation to form dark mixed hydroxide precipitates. These hydroxides form complexes under aqueous conditions and under specified conditions, resulting in magnetic compounds predominantly ferrites. Although ferrites are hardly soluble in water, easily separable by sedimentation, filtration and magnetic separation, they could be an ideal process for wastewater treatment or for the capture of valuable metals in the production process eg Be, Sr, Br, Mo, Ni, Co, Cu, Ge, Ga, Ti, the method is not yet sufficiently widespread because the solutions and waste water used do not simultaneously separate anions, in particular SO ^{2 -} , but on the contrary are further enriched with alkali metal ions. Solutions after separation of metals are therefore very saline • and cannot be ¹ without; other difficult adjustments to be discharged into the Waterscape or otherwise utilized;

The deficiencies of both the purification processes have been eliminated or the separation of the metals has been eliminated by the process according to the invention. The substrate is that the suspension of the solid insoluble neutralization product is oxidized by atmospheric oxygen at a temperature of from 40 ° C to 100 ° C, in all or lesser volume, by sedimentation in a gravitational or centrifugal field.

In particular, the advantages of the method according to the invention are:

1. - the amount of soluble salts in the solution does not increase as is the case with alkali metal hydroxide precipitation,

2. are ¹ sulfates removed and? precipitated db ',

3. a magnetic sediment is obtained which can be captured by magnetic separators and used in the production of ferrites or their treatment into pure metals;

4. strongly toxic bivalent metals. they are shown to be stable in the solubility of the precipitate which can be stored in landfills.

By applying a new waste water treatment process, eg mining and metallurgical and chemical plants; containing predominantly divalent and optionally trivalent metal ions, their pH is adjusted by the use of an aqueous suspension of quicklime or burnt dolomite _; or mixtures thereof to a value of 7 to 12, preferably 10. Burnt lime or burnt dolomite may be partially replaced by the preliminary use of finely ground limestone or dolomite up to a pH of 6-7. The waters do not contain cations of the two. metal ions, iron ions, or * cations, other double metal * with the advantage of * magnesium, are added to the solution, according to the metric ratio required for the formation of · ferrites, · divalent iron can be "catalyzed". this solution by a partial reduction of trivalent iron in the treated water. If iron ions are not present in the waste water, either it is necessary to add either a straight or a red-triple-iron iron to a twenty-strong, preferably leakage, layer. coal. or r-containing lower sulfur oxidants such as pyrite.

The resulting precipitate slurry ** is further heated to a temperature above < 40 ° C (if it is not already at this temperature; heated before neutralization) and is further slowly oxidized in the precipitate. with oxygen, stirring constantly until it is formed. precipitate with magnetic; properties. If the waste waters contain alkali metal ions, a precipitate is formed with magnesia properties already at a temperature above above especially after a maturation time of 10 min. up to 24 hours. preferably 1 hour.

The process according to the invention can be advantageous in that the volume of the suspension of the solid · insoluble neutralization product is reduced by sedimentation in a gravitational or centrifugal field before heating and oxidation.

In order to avoid having to heat the entire volume of wastewater to the desired temperature, the precipitate slurry may preferably be left to sediment in a gravitational or centrifugal field after addition of lime, magnesium or iron ions so that the sediment volume is reduced to 1-90% of the original wastewater volume. This reduced volume is then further processed by heating and oxidizing with air oxygen according to the foregoing procedure.

During oxidation and possibly maturation, a granular suspension is formed which is well sedimentable and filterable and has good magnetic properties. All of these properties can be utilized in solid and liquid phase separation, preferably magnetic separating properties in a magnetic separator with induction of a magnetic field above 0.005 Tas preferably under laminar flow conditions. Under these conditions, non-magnetic particles such as calcium sulfate remain adsorbed on the magnetic particles and are trapped together in a magnetic separator. In order to obtain pure compounds of divalent and trivalent metals, either the concentrate obtained is separated further in a magnetic separator under turbulent conditions or this separation is already carried out with the original suspension in the first stage.

The residual sulphate contents in the clarified water correspond to the solubility of their calcium salts, i.e. about 1.5 g / l. In order to further reduce their content, it is necessary to use a second purification stage, eg with barium salts. Since in this second stage the solution is already free of further impurities, in particular Fe ions, the precipitant used can be well regenerated and its consumption is low.

The following are exemplary embodiments

of the method of the invention.

Example 1

Mine water from surface brown coal mines at pH 2.1 and 0.79 g / l of ferrous iron and 0.46 g / l of ferrous iron in the form of sulphates contains a total dry matter of 5.63 g / l. According to spectral analysis, this dry matter contains in addition to iron ions 1 to 10 why. Al, Ca, Mg, 0.1 to 1.0% Mn, Zn, Si, Na, 0.01 to 0.1% As, B, Co, K, 0.001 to 0.01% Ba, Be, Ni, V, Sr, Ti and below 0.001% Cu, Ge, Pb, U. To this mine water is added 2.65 g magnesium sulphate per 1 l and lime milk (300 g CaO villas of milk), up to pH 10 Next, the suspension is heated to 50 ° C and air is bubbled through at a rate of 1 L per minute. per 1 mine water for 22 min. The resulting precipitate is separated quantitatively in a magnetic separator upon induction of magn. field 0.0214 T. Clarified water. it contains 0 mg / Fe, 0,01 mg / l As, 1,55 mg / ml of SO2 ^2- and less than 0,01 mg / l of metals.

Example 2

Mine water of the same composition as in Example 1 is basified with a lime suspension to pH 11.9 and allowed to sediment up to 1/3 of the original volume. After separating 2/3 of the clarified water, the sedimented slurry is heated to a temperature above 75 ° C and bubbled through for 15 min. 1 1 air per min. per 1 l of suspension. The precipitate is filtered on a drum filter. The composition of the clarified water is 0 mg / l Fe, 0.02 mg / l As, 1.5 mg / ml SO4 ² and less than 0.01 g / l other metals.

Claims (1)

SUBJECT Process for the purification of waste acidic water resulting from the extraction, treatment and processing of mineral resources by neutralization with limestone or dolomite or their firing products containing divalent or trivalent metal cations containing iron and sulphate anions or to which divalent or trivalent metal cations are added containing iron or the invention of cations of other divalent metals, preferably magnesium, in order to achieve the stoichiometric ratio required for the formation of frits, characterized in that the solid insoluble neutralization product suspension is oxidized at atmospheric oxygen at 40 to 100 ° C in whole or reduced the volume of sedimentation in a gravitational or centrifugal field.