DE102004006084A1 - Process to render acidic water or water containing sulphate effluent from mining suitable for safe disposal or further use - Google Patents

Abstract

In a process to treat acid water or water containing sulphate effluent from mining operations, the water is first mixed and reacts with plaster and resulting in precipitation of calcite particles. The calcite particles are then subject to biochemical sulphate reaction to precipitate iron sulphide from which calcite is precipitated by de-gassing. The precipitated calcite is surrendered to the incoming feed of acid and/or sulphate liquid effluent. The treated water is then further treated by reversal of pyrite efflorescence by microbial sulphate reduction and precipitation of solid sulphides, causing a biochemical sulphate reduction. In a further process stage biological calcite precipitation is driven by de-gassing carbonic acid and escape of the gas to the atmosphere. Also claimed is a suitable water treatment assembly.

Description

The The invention relates to a method and an arrangement for treatment acidic and sulphate wastewaters, for one while from mining to over Days arrive, on the other hand also in the area of such areas in which after completion of mining measures, in particular the lignite mining, again original largely natural conditions to shape.

In particular, after aeration of the substrate by the lignite mining run in the underground from a number of processes that characterize the nature of the so-called tipping groundwater. These are chemical and biogeochemical reactions that serve to acidify seepage and groundwaters. Thus, the iron sulphides which are stable in their natural state in anerobic groundwater are subject to weathering by oxidation in contact with oxygen:

The forming waters are mainly due to high iron and sulphate contents and high acid loadings characterized.

Also Lakes that are created in former opencast mines are affected. Once the groundwater has risen again, natural outflow conditions are again posed but this is in trenches and source areas ventilated Kippengrundwasser extremely acidified and sulphate contaminated. This water pollutes the downstream receiving waters and is well-known usual To feed mine water purification plants.

• – Sulfat verhält sich weitgehend konservativ. Übliche Grenzwerte für Trinkwasser werden um ein mehrfaches überschritten. Dadurch treten bereits erwähnte Korrosionsprobleme an Betonbauwerken auf.
• – Nach Zugabe von Kalk (CaO) verbleibt eine sehr hohe Resthärte (>10 mmol/L ~ 56°dH).
• – Bei der hohen Calciumkonzentration fällt pufferndes Hydrogencarbonat bereits im Neutralbereich als Calcit aus. Die Pufferung liegt meist unter 0,6 mmol/L. Dadurch reichen bereits geringe Säureeinträge für eine Wiederversauerung aus.

Very often, therefore, a neutralization by liming is made by the present mainly in the form of hydrogen, hydrogen sulfate and iron ions present acid is neutralized. It already precipitates plaster. The potentially acid rock bottomwater flowing into the open-pit mines is therefore often saturated with gypsum. The disadvantage here is that the sulphate concentration is retained by the neutralized groundwater having essentially the following constitutional disadvantages:

• - Sulfate behaves largely conservatively. Usual limits for drinking water are exceeded by a multiple. As a result, already mentioned corrosion problems on concrete structures occur.
• - After addition of lime (CaO) remains a very high residual hardness (> 10 mmol / L ~ 56 ° dH).
• At the high calcium concentration, buffering bicarbonate already precipitates as calcite in the neutral range. The buffering is usually below 0.6 mmol / L. As a result, even low acid inputs are sufficient for re-acidification.

These Situation has led to the development of various specific procedures guided. Thus, according to the US-PS 6,174,444 and 5,698,107 the electrochemical Neutralization applied, with the contained sulfate and metal ions precipitated become. Other suggestions Provide natural acid dissolving in acid wastewater Bacteria to settle (US Patent 6,325,923) or oxidation-promoting In their growth to inhibit microorganisms (US Patent 5,171,454). To the One is the effort considerably if it is a multi-level On the other hand takes place in a one-step process only an imperfect treatment.

One in Germany widespread procedure is the external water discharge in Tagebauseen to the natural Carbonate buffer of surface water to use. This procedure is ongoing time very stretched, with very much the external water discharge as well often is not sufficient to compensate for the successful acid entry.

task The invention therefore relates to a method and an arrangement develop, with the help of which effort in the recovery the original one Properties of natural water from acidic and sulphate contaminated effluents of the Mining is further reduced and the sulfate and calcium concentration on a measure as befits Domestic hot water usual is, can be lowered.

The Task is solved for the treatment of acidic and sulphate mining wastewater first a gypsum precipitation carried out and resulting gypsum sludge is discharged after failures.

There approximating the mining wastewater gypsum-saturated Part of the sulfate can be by increasing the calcium concentration precipitated as gypsum become. When using calcite, a partial deacidification takes place at the same time. At pH ~ 2 is half of the sulfate as hydrogen sulfate. As a result, more gypsum is soluble than at neutral pH. This gypsum can already be neutralized precipitated become. At the same time, the pH value becomes the optimum of sulfate reduction approximated. Parallel falls also iron (III) hydroxide in flake form. The flow is Therefore, here designed so that only gypsum crystals sediment. This is done with appropriate turbulence, the example already by inflowing Mining wastewater is generated relatively quickly, so that only the gebil Deten Iron hydroxide flakes suspended in the process sequence subsequent substrate are abandoned.

Here there is a further treatment of the mining wastewater by reversal the Pyrite weathering by sulfate reduction by microorganisms under precipitation Solid sulfides, so that a biochemical sulfate reduction occurs. With it changed the existing in the mining waste water iron hydroxide due to Passing the substrate to iron sulfide which separates after precipitation is caught. At the same time, carbon is being produced also lead to gas excretion can and which is subsequently discharged to the atmosphere. Therefore the mining wastewater is given up by flowing vertically through the substrate. As a result, the treated water is under a higher hydrostatic Pressure that counteracts gas bubble formation. Because the mining wastewater in the described intermediate no longer the stoichiometric must have the necessary amount of iron, the process in this second Stage iron hydroxide in the form of Wasserwerksschlämmen or water sediments supplied become.

In detail, the following possible reaction paths result in the parameter space pH-NP with phase-stabilized regions:

First, will at (1) the solved Oxygen consumes the anaeroby with reduction of iron (III) too Iron (11) set and the neutralization product remains unchanged. at (2) uses sulfate reduction. Acid is consumed, the pH rises and formed carbon dioxide falls with the iron (11) as Siderite out. With hydrogen sulphide, iron (11) precipitates as iron sulphide off and the concentration dissolved Hydrogen sulfide gas decreases rapidly with increasing pH. In (3), the pH stabilizes around pH> 8 in phase equilibrium with siderite / iron hydroxide minerals. Formed carbon dioxide falls immediately as iron carbonate. In (4) falls in weakly alkaline Milieu calcite off and the pH is slightly higher by siderite / iron hydroxide / calcite mineral phases stabilized. Because of low equilibrium concentration of bicarbonate or the carbonate is the reaction solution during this phase with NP = 0 almost unbuffered. In (5) becomes after depletion of the Eisenhydroxidvorrats formed siderite converted into sulfide and inorganic carbon mainly precipitated as calcite. The decreasing pH is mainly due to the calcite balance certainly. At (6) is running after reduction of the total sulfate to sulfide-sulfur the reaction further.

Iron feed and pH are controlled so that only little hydrogen sulfide is produced. The water leaving the substrate is strongly hydrogencarbonate-buffered. Resulting iron sulfide sludge is withdrawn. Residual substrate to be degraded when passing the anaerobic reactor and algal biomass formed who the. As a result, in a further stage, a biological calcite precipitation subsequently occurs via degassing of the carbonic acid which escapes into the atmosphere. Through photosynthesis, this Calcitfällung be supported, as a result of which a biogenic descaling occurs. The precipitated in the process of Calcidfällung in its entirety and biomas seangereicherte calcite is fed back to the inlet of the acidic and sulphate mining wastewater before the start of the process described so far.

The Procedure consists in so far of three stages, which are in their effect complete, by first a Gypsum precipitation, subsequently followed by a sulfate reduction and finally the calcite precipitation he follows. The resulting after the outgassing of carbon dioxide is water softened by sulphate reduced and sufficiently hydrogencarbonate buffered as well biologically stabilized. It is in a quality that safely supplied to the flood can be.

In the sulfate reduction can as a resource iron hydroxide-rich sludge of water treatment in Combination with easily degradable products of the food industry and / or agriculture.

Waste incurred Iron sulphide slurry is preferably anaerobically for further use landfilled. The resulting iron sulfide sludge can also be used as an aggregate the production of sulfuric acid and / or as a precursor to the cement industry become.

A to carry out of the inventive Procedure designed arrangement initially has an open-topped horizontal perfused flat container, which may also be a channel, with a one-sided inclined Ground up. In the vicinity the entry of acid and sulphate mining wastewater can an introduction device for Calcite sludge be formed, if not otherwise abandoned becomes. By in the further flat design of the flat container a big surface for the assigned gypsum-saturated Wastewater present so that precipitated gypsum components sediment can. About the Effect of unilaterally inclined soil is at the lowest point of the flat container a concentration of the precipitated Gypsum sludge available. While For smaller systems, this gypsum slurry can be removed manually can, is at a greater dimensioned design of the plant at the lowest point one Outlet device for Gypsum slurry is formed to remove this gypsum slurry and one further use to be able to. This outlet device can also with a trigger device be combined, which is either integrated or downstream.

the flowed through horizontally flat container is a downhill flowed through with supporting bodies and a substrate filled and downstream as an anaerobic reactor vessel, the first a the inlet of the upstream flat container substantially opposite overflow of the upstream flat container associated entrance. This entry is designed that the mining wastewater to be neutralized on the in the anaerobic reactor accumulate introduced substrate and penetrate this downwards can. This anaerobic reactor has a laterally disposed over its whole length reaching channel with free cross section on the ground area of the anaerobic reactor a junction has and at the top of a drain, which in a further flat downstream of the anaerobic reactor open top flat container opens. At the Bottom of the anaerobic reactor sedimenting iron sulfide sludge is skimmed off, provided not in turn dependent of the size the plant is designed a trigger device. The anaerobic reactor leaving water rises in the free cross section of the channel and occurs over the upper end of existing flow in the subordinate above open container one. Through the large surface that exists here again, as already described, a biological Calcitfällung, wherein the calcite sludge must be redirected to the input area should. That's why the open top flat container again over a sloping soil formation that is the collection of this calcite sludge at a low point and thus allows its removal. The preferred solution plans to train here again a trigger device that at Large plants with considerable throughput over a pipeline with a purpose trained funding agency with the inlet region of the anaerobic reactor upstream flat container connected is. Furthermore, this has the anaerobic reactor downstream top open flat container a flow for the introduction of the invention treated mining wastewater in the receiving waters.

The effective depth of the anaerobic reactor is regularly greater than its width and can be a multiple of this. Similarly, all outlets with Deduction facilities, such as pumps and the like, be provided. Likewise, a multiplication of the described training and their individual elements in combination with each other possible.

at a naturalistic education of the system, this is very good in the Landscape.

The Invention will be explained in more detail below using an exemplary embodiment.

The associated Drawing shows as

1 the functional diagram of an inventively designed system.

In a shallow container 1 embedded in the ground flush with the earth's surface, the water is introduced from a source of about every hour 3 Cubic meters of an acidic sulphate-containing wastewater.

The depth of the shallow tank 1 is immediately in the region of the introduction 10 cm; the bottom slants towards the opposite side of the preamble and reaches a depth of 60 cm, making it a swamp 2 arises. Its volume is such that a residence time of about one hour is not exceeded, since the gypsum precipitation can be delayed.

Introduced acidic and sulphate contaminated water is mixed with precipitated calcite sludge to form gypsum slurry, which is located in the deepest part of the shallow tank 1 So the swamp 2 , settles. This settled gypsum slurry is removed mechanically by hand.

Above the area of the lowest point of the shallow tank 1 is an overflow 3 formed, the passage of the water into a subsequently embedded in the soil anaerobic reactor 4 allows. This has a diameter of 2.5 m and a usable depth of at least 2.5 m, so that a residence time of the water of approximately at least half a day results. Furthermore, the anaerobic reactor 4 provided with suitable packing. These packings may be exemplified by vegetable wastes or other pellets made from suitable waste materials for this purpose. Likewise, substrate is filled. These are, for example, liquid waste from agriculture. If an amount of 8 mmol / L methanol is added to an extremely acidic groundwater, this will replace the addition of approximately 380 g / cubic meter of biochemical oxygen demand.

This when filling the anaerobic reactor 4 from the shallow container 1 Exceeding water may contain traces of hydrogen sulfide, as sulfate is reduced to HS. Therefore, as a precaution, a non-illustrated biological odor filter is formed as a cover over which the exhaust air is passed in order to avoid the occurrence of unpleasant odors. After oxygen entry, excess substrate and sulfide sulfur are also degraded.

Laterally in the anaerobic reactor 4 is a channel leading from its bottom to the turf sole 5 formed with a free cross-section, near the bottom of the anaerobic reactor 4 one after the interior of the anaerobic reactor 4 is designed to directed inlet having. This channel 5 is exemplary in the interior of the anaerobic reactor 4 trained, but it can also be arranged on the outside thereof, in turn, with its lower mouth to the lower interior of the anaerobic reactor 4 connected is. Likewise, in the bottom of the anaerobic reactor 4 a withdrawal device for precipitated iron sulfide sludge present. This is an example of a mobile fecal pump 6 ,

The upper outlet of the canal 5 allows the transfer of ascending liquid in a downstream flat and open-topped container 7 ,

After precipitation of the Eisensulfidschlammes increases through the existing hydrostatic pressure, the water through the free cross section of the channel 5 upwards and enters the flat and open top flat container 7 one. This has in terms of its internal design as well as the flat container 1 a sloping ground, so that at the lowest point in turn a swamp 2 to collect precipitated compounds. The entry of the water is over the flat area, the outlet is as a drain 8th formed, over which the water in the secondary flow over. Its volume is such that it gives a residence time for an after-reaction of about 8 hours.

container 1 and container 7 can be designed close to nature and be set up in a flow section before and after the anaerobic reactor. In particular container 7 can be used as a channel or as Schö be formed.

In the open-topped container 7 caused by the turn in relation to the volume in turn large surface, a precipitation of calcite. This Calcitausfällung in the described post-reaction can be supported by photosynthesis (biogenic decalcification). Since the Calcitfällung should be supported biologically, the longest possible residence time should be sought. By integration into the natural drain only a small construction cost is required.

Precipitated calcite is recovered manually and discontinuously after the flat container 1 spent.

It is in all embodiments, especially with a bigger one dimensioned design, possible, Conveyors use. The skill For example, sludge or fecal pumps, extraction screws or other suitable conveying organs be.

After the original acidic and sulphate-containing water over the drain 8th the open top flat container 7 has left, it has the correct design of the inventive arrangement to dhw quality.

1

flat container

2

swamp

 3

overflow

4

anaerobic reactor

5

channel

 6

Fäkalpumpe

7

above open flat container

 8th

procedure

Claims (20)

Process for the treatment of acidic and sulphate-containing sewerage of mining, in which - first one gypsum precipitation carried out and resulting gypsum sludge is discharged after failures, in a subsequent step - one biochemical sulfate reduction takes place and an iron sulfide precipitation made in the Resulting ferrous sulphide sludge is discharged, in another Stage afterwards - over a Degassing a calcite precipitation done and - the in the step of Calcidfällung precipitated Calcite the feed of acid and sulphate mining wastewater is given up again. The method of claim 1, wherein - as operating resources for the Sulphate reduction a biologically utilizable substrate with anaerobic Environment is used. The method of claim 2, wherein - in the Sulfatreduktion as resources iron hydroxide-rich sludge the Water treatment can be used. The method of claim 2, wherein - in the Sulfate reduction as a resource readily degradable products of Food industry be used. The method of claim 2, wherein - in the Sulfate reduction as a resource readily degradable products of Agriculture are used. Method according to one of claims 1 to 5, in which - the biochemical Sulftareduction is carried out running in the vertical direction. Method according to one of claims 1 to 6, in which - The Calcitfällung is supported by photosynthesis. Method according to one of claims 1 to 7, in which - excess calcite sludge used for mine water neutralization. Method according to one of claims 1 to 8, in which - excess calcite sludge provided as an agricultural by-product. Method according to one of claims 1 to 9, wherein - the accruing Iron sulfide sludge is anaerobically dumped. Method according to one of claims 1 to 10, in which - the accruing Iron sulfide sludge as an additive of sulfuric acid production to disposal is provided. Method according to one of claims 1 to 10, in which - the accruing Iron sulfide sludge provided as a precursor of the cement industry becomes. Arrangement for carrying out the method according to one of claims 1 to 12, in which - initially a horizontally flow-through, flat top and provided with a feed for mining wastewater ( 1 ) - with a unilaterally inclined bottom is present, so that at the lowest point gypsum sludge can collect, and - on one side over the flat part an inlet is formed, - the inlet opposite one with the entry into a filled with packing and substrate anaerobic reactor ( 4 ) connected overflow ( 3 ), - the anaerobic reactor ( 4 ) starting at the bottom and rising upwards and there provided with a free outlet channel ( 5 ) with free cross-section, - the residual space of the anaerobic reactor ( 4 ) is filled with packing and substrate, - at the upper end of the channel ( 5 ) the outlet is formed as a transfer, which in another the anaerobic reactor ( 4 ) nachgeord net open top flat container ( 7 ) at the lowest point of the anaerobic reactor ( 4 ) an outlet for sedimenting iron sulfide sludge is formed, - the subordinate flat container open at the top ( 7 ) has an inclined bottom formation for collecting the sediment, and - in the vicinity of and above this lowest point of the flat container open at the top ( 7 ) again a sequence which preferably flows into the continuing receiving flow ( 9 ) is trained. Arrangement according to claim 13, in which - at least one of the deepest points of the horizontal through-flow and provided with a supply for mining waste water flat container ( 1 ) and the flat container ( 7 ) An outlet is formed. Arrangement according to claim 14, in which - at least one of the outlets a trigger device is formed. Arrangement according to claim 15, in which - the extraction device of the flat container open at the top ( 7 ) with the feed of the anaerobic reactor ( 4 ) upstream flat container ( 1 ) connected is. Arrangement according to one of claims 13 to 16, in which - the effective depth of the anaerobic reactor ( 4 ) is greater than its horizontal extent. Arrangement according to one of claims 13 to 17, in which - several of the anaerobic reactors ( 4 ) upstream flat containers ( 1 ) are formed. Arrangement according to one of claims 13 to 18, in which - parallel to a plurality of anaerobic reactors ( 4 ) are formed. Arrangement according to one of claims 13 to 19, in which - several flat containers open at the top ( 7 ) are formed.