DE3039660A1 - METHOD FOR THE DAMAGED DEPOSIT OF THICKEN ACID ON LAND - Google Patents

Description

Procedure for safe disposal

of dilute acid on land The invention relates to a method for harmless Landfilling of dilute acid.

E.g. in the production of titanium dioxide and in the production of colorants There are considerable amounts of liquid containing sulfuric acid and, in some cases, iron sulphate Waste materials commonly referred to as dilute acid. Alone to them According to statistical data, the Federal Republic of Germany has around 2 per year Million t from titanium dioxide production and 0.3 million t from dye production.

Landfilling these liquid waste products is because of theirs high acid content and the content of accompanying heavy metals are not permitted. Tables 1 and 2 show average analyzes of thin acids.

The recovery of sulfuric acid is only possible with a high expenditure of energy feasible and economically uninteresting due to the lack of sales opportunities. the Neutralization of the dilute acid would be technically feasible, but it would take up large areas for the disposal of the resulting gypsum and iron hydroxide mixture.

In the current state of the art, this is the disposal method therefore it is mainly the introduction of the dilute acid into the sea that is used. This kind the disposal of waste at sea (dumping) takes place by the Federal Republic of Germany åus mainly off the Dutch coast and in the Heligoland sea area instead of.

The dumping of dilute acid is said to be reduced in the future and eventually be completely omitted (Directive of the European Community, 1978). Decisive for this purpose, ecological studies on possible harmful effects are mainly on the marine environment. A summarizing view of those brought into the North Sea Waste materials and its ecological impact is in the report Environmental Problems of the North Sea " recently presented by the Council of Environmental Experts has been.

The object of the invention is to provide a method for a harmless Landfilling of dilute acid on land too.

enable.

To solve this problem it is proposed according to the invention that the dilute acid is mixed with lignite ash and the mixture is stirred and that the proportions are adjusted so that the dilute acid is neutralized and the mixture becomes hard.

If the proportions are set correctly, depending on the iron sulphate content and acid concentration of the dilute acid as well as the CaO content of the ash can fluctuate, If the dilute acid is neutralized on the one hand, a solid, inert one is created on the other and relatively waterproof material.

Lignite power plant ash is preferably used as the ash occurs in large quantities and also has problems when depositing because their sulphate components get into the groundwater in unacceptably large quantities reach.

Both dusty, ashes that are not humidified, such as those obtained in the bunkers of the power plants, as well as humidified ones Power plant ash, such as that found in the opencast mines of the Rhenish lignite mining area comes to tilt.

This power plant ash is composed of the mineral substance the pure coal and from the sand and clay admixtures conveyed during the mining of the coal.

Most of this ash consists of very fine-grained electrostatic precipitator ash, the smaller one made of coarse-grained, sandy boiler ash.

For the chemical and physical behavior of the power plant ash its calcium content is of crucial importance. It is present as calcium oxide, ferrite and sulfate. The high responsiveness is due to the fine grain of the Ash and its large inner surface are reinforced.

To neutralize the dilute acid and to achieve a solid end product with the lowest possible water permeability, it is necessary to use the dilute acid with ashes to mix in a certain weight ratio and stir until it has a mushy consistency. With a medium CaO content the power plant ash of about 10 wt .-% and a H2S04 concentration of the dilute acid an average of about 12% has a mixing ratio of 100 parts by weight Ash to 60 to 65 parts by weight of dilute acid proved advantageous.

Lower CaO content in the ash or higher acid or iron sulphate concentrations of the dilute acid make a dilution with water necessary, since in every case a pulpy consistency of the mixture must arise.

The pulpy mixture formed from ash and dilute acid, which is caused by mechanical effects (shaking, driving on with caterpillars or rollers) are further compressed can be cemented after a short time as a result of the chemical reactions that go on under warming. The main ones are as follows Reactions: 1. Neutralization of the acid (schematic) 5H2S04 + 3CaO + Ca2Fe205 + 8H20 = 5CaSO4 2H20 + 2Fe (OH) 2nd reaction of the excess ash with water and later with carbonic acid CaS04 + 2H20 = CaSO4. 2 H20 Ca2Fe2O5 + CaO + 6H20 = 3Ca (OH) 2 + 2Fe (OH) 3 Ca (0) 2 + C02 = CaCO3 + H20 By reaction of the in the Thin acid from the titanium dioxide production contained iron sulfate with the ash gypsum and iron (II) hydroxide are formed; the latter settles when oxygen enters to ferric hydroxide.

The invention solves two problems at once by the safe dumping of not only dilute acid, but also power station ash is made possible.

Due to the very low water permeability of the solidified Ash-dilute acid mixture can also be the sulphates of the ashes from rain or groundwater can no longer be extracted.

It should also be used to bind the heavy metals contained in the thin acid the mixture can be so composed that it becomes basic. A detachment of the Heavy metals are prevented to such an extent that they pose a threat to the groundwater can be excluded.

When mixing thin acid and power plant ash, i.e. two basically different waste materials, is created by the method according to the invention a new solid waste product that, due to its consistency, is suitable for landfill is suitable on land.

The physical properties of the new waste product will be through characterized by a very low water permeability.

The heavy metals contained in the dilute acid are in the new waste material either precipitated or sorbed, causing a relevant leaching of pollutants is not to be worried about. Therefore, it is safe to deposit the dilute acid on land possible. A chemical further treatment of the dilute acid, which with high investment costs, considerable expenditure of energy and special measures for the elimination of the resulting Hazardous waste is associated, is dispensable by the method according to the invention.

When using the method according to the invention, the can here as Waste material produced by the end product without special precautions at low cost be housed in any organized landfill.

The large-scale application can take place in that the ashes Transported separately via conveyors and the dilute acid via pipelines will. These two components are brought together in a mixing plant, immediately before landfilling of the inert waste product created here. Feeding, mixing and discharge should be able to take place continuously. The mixing plant can be advantageous can be attached to a movable drop-off gate.

beyond the environmentally friendly disposal of the dilute acid the procedure has other notable advantages. For example, the numerous, sand and gravel pits near the Rhine as well as other abandoned ones On conclusions to be filled with this inert waste product. Because of the extreme Differences in water permeability between the introduced waste material and the natural environment, the landfills would be neither from the groundwater nor from the Surface water flowing through it. This fact would - in addition to the chemical Binding of pollutants - another guarantee that an impairment of the groundwater can be almost ruled out. The landfills can eventually are covered with natural soil material, so that the newly gained areas are available again for any use.

Example mixtures of brown coal power plant ash and 12% dilute acid in a ratio of 100: 60 to 65 were placed in 100 ml steel cylinders, the bottom of which were closed by plastic caps, filled and compacted by shaking.

After a few days, the samples were placed in the Ef apparatus according to I.E. Wit - at a differential pressure of about 10 mm Water column - on investigated their water permeability.

The results are shown in Table 3.

To determine the substances that can be eluted from the new waste product, especially with regard to the heavy metals contained in the dilute acid Leaching tests according to the current guidelines (RdErl. D.

Minister for Food, Agriculture and Forests v.

July 21, 1977-I1IC8-902 / 4-25459-MBl.NW. 1977 p. 1125). In addition 300 g test specimens with 10 times the amount of distilled water 24 Treated for hours with constant water circulation. The evaporated residue the clear filtrate was then analyzed. The result is shown in Table 4.

Tab. 1: Average analyzes of thin acids of various origins from the digestion of ilmenite (a, b) or Sorel slag (c) (source: Deutsches Hydrographisches Institute) (c) Quantities up to 470,000 t / a up to 750,000 t / a up to 600,000 t / a pll value below 1 under 1 under 1 COD approx. 7 g 0 O2 / l approx. 9 g 02/1 approx. 5 g 02/1 H2SO4, free approx. 12 % approx. 12% approx. 23 TiOSO4 approx. 1.0% approx. 0.8% not mentioned MgSO4 approx. 2.0% approx. 1.0 % "MnSO approx. 0.1 96 approx. 0.07%% Al2 (SO4) 3 not specified max. 0.2%" Na2SO4 "" max. 0.03% "CaSO4" "max. 0.07%" iron max. 50,000 mg / l approx. 65,000 mg / l max. 2.1% vanadium max. 350 "approx. 110" max. 0.05 96 chromium max. 200 "max. 200" max. 0.03% zinc max. 20 max. 40 "max. 80 mg / l lead max. 2" max. 2 "max. 10 nickel not mentioned approx. 15 "max. 3 copper max. 1.5" max. + 1.5 "max. 2 Cadmiun n.n. ++ n.n. ++ max. 0.2 "mercury n.n. +++ n.n. +++ max. 0.03" arsenic n.n. n.n. n.n.

n.n. = not detectable above the detection limit: detection limit 0.1 mg / l detection limit 0.01 detection limit 0.1 Tab. 2: Average analysis of thin acids from dye production (source: Umweltprobleme der Nordsee. - Opinion of the Council of Experts on Environmental Issues, 1980) H2SO4 Benzene-, Naphthalene and anthraquinone sulionic acids 1 96 Fe 100 ppm Cr Cu, Zn 1 - 10 Ni, V, Pb, Hg 0.1-1 As, Cd, Ag <0.1 organohalogens 10 Tab. 3: Water permeability (Kf in m / s) of test specimens made of ash and dilute acid in a weight ratio of 100: 60 100: 65 5.4. 10 8 9.1. 10 8 9.3. 9.3 x 10-8 7.2. 10-8 1.4 x 10-7 1.0 4.6 x 10-8 2.5 3.9. 3.9 x 10-8 1.2. 10 1.0 x 10-7 1.0 8.6 x 10-8 1.0 4.5 x 10-7 2.3 1.0 x 10-7 2.4 3.2 x 10-8 4.9 2.3 x 10-8 4.5 2.8. 10 8 4.4. 10 8 1.6 x 10-8 2.5 1.6 Tab. 4: Elution of test specimens from ash and thin acid . From titanium dioxide production, evaporation residue 420 of which CaSO4 295 vanadium <0.0 Chromium <0.0 Nickel <0.0 Copper <0.0 Zinc <0.0 Biel <0.0

Claims (5)

Claims 4; '. Process for the safe disposal of thin acids on land, d u r c h e k e n n z e i c h -n e t that the dilute acid with lignite ash mixed and the mixture is stirred and that the proportions are adjusted be that the dilute acid is neutralized and the mixture hardens. 2. The method of claim 1, d a d u r c h g e -k e n n z e i c N e t that CaO-containing lignite power plant ash is used. 3. The method according to claim 2, d a d u r c h g e -k e n n z e i c n e t that the mixture in the ratio of about 100 parts by weight of brown coal power plant ash is composed with about 60 to 65 parts by weight of dilute acid. 4. The method according to any one of claims 1 to 3, d a -d u r c h g e does not indicate that water is added to the mixture. 5. The method according to any one of claims 1 to 4, d a -d u r c h g e I do not note that lignite ash in such an amount with the dilute acid is mixed so that the mixture binds the heavy metals contained in the thin acid shows basic reaction.