DE4217987A1 - Removal and recovery of heavy metals from earth, sludges and waterways - by amalgamation and sedimentation of esp. mercury@, nickel@ and cobalt@ and their cpds., by addn. of powered zinc@ or aluminium@ - Google Patents

Abstract

Heavy meatls, esp. Hg or its cpds. and salts of Ni and Co and their cpds., are removed from earth, sludges and waterways by a process in which the heavy metals and/or their cpds. undergo amalgamation in aqueous suspensions of said earth, sludge or water, and are removed by sedimentation. Pref., amalgamation is caused by the addn. of powdered Zn, Al or their alloys to the suspension, which is subjected to ultrasonic radiation during amalgamation. USE/ADVANTAGE - As well as removal from contaminated earth, etc., recovery of pure forms of Hg and other substances is also possible.

Description

The invention relates to a method for separating Heavy metals, especially in the form of mercury, nickel and cobalt from the ground, mud or water.

There are essentially three methods for removing Heavy metals, from contaminated soils, sludges etc., with which in particular also those contaminated with mercury Soils could be disposed of, which is a major problem put.

• 1. Thermal processes are state of the art. They can be used universally, but are also the most complex due to the development of dust and the need to clean the exhaust gas. The costs are given as about 200 to 500 DM / Mg soil.
  Thermal processes for mercury separation are not without controversy, because emissions cannot be ruled out here or are at least feared. Thermal on-site processes are difficult to implement; Off-site processes require the transport of the contaminated soil as special waste.
• 2. Previously proposed electrochemical in-situ processes use the migration of ions or particles (electrophoresis) in the electric field. In laboratory tests, a depletion of 60% was achieved with an energy requirement of 100 kWh / Mg. The rate of migration is, however, low (5x10 ^-9 m / V · s) that long decontamination times result, namely weeks to months.
  Problems of an electrochemical in-situ process that are recognizable today are:
  • - Only dissolved mercury can be separated
  • - Inhomogeneities in the soil lead to uneven migration speeds; preferred paths are formed.
  • - Changes in the pH value in the vicinity of the electrodes lead to precipitations (fouling) after a short period of operation which impair proper operation.
• 3. Treatment of the soil with complexing agents so that mercury silver ions are bound. These are then through Extraction separated. Another disadvantage is that only dissolved mercury can be detected. In addition, must the floor can be treated with large amounts of solution.

The invention has for its object an improved Process for the separation of heavy metals from the earth rich to indicate sludge or water, that in particular is suitable for the separation of mercury.

This object is the subject of the claim 1 solved. After that, he will make decisive progress aims by pulling over the excavated earth quantities or sludges and possibly water (if these do not already form a suspension) in an aqueous Suspension an amalgamation is carried out. Through this Measure can not only mercury but also in particular nickel-II and cobalt salts in the presence of mercury and its salt in a form that is easy to sediment be transferred.  

This also makes it possible to use all those containing mercury Compounds and also to capture the elementary mercury sen. The same applies to the other amalgamable heavy metal salts. Amalgamation can be done in a simple manner Add powder of zinc or aluminum-containing zinc alloys or zinc salts. The ones from there elemental mercury and its compounds Zinc and aluminum amalgams are characterized by a large Resistance in water. This also applies to the amalgams made of nickel and cobalt.

A particular advantage of the method according to the invention is that it opens up the possibility Mercury as well as the other substances not only work effectively remove, but also recover in pure form.

It is precisely through amalgamation that it is possible through a multiple sedimentation or other mechanical separation processes like solid phase separation on vibrators a complete ent to effect distance. Although with the high density of the heavy metal mercury itself without the measure of Amalgamation will expect good sedimentation is likely, it is still almost impossible to stir small-sized mercury droplets and in particular mercury compound sufficient in sedimentation to capture. Also adsorption on soil or sludge parts celn stands for a successful mechanical separation opposite.

In contrast, the amalgams formed from zinc and aluminum can be easily separated by known density sorting methods, in particular sedimentation. Sedimentation is usually used to determine the grain size of dispersoids (sedimentation analysis for grain sizes <40 µ) or for solid-liquid separation. However, since the sedimentation speed depends not only on the grain volume but also on the density difference of the solid and liquid phase, solid-solid separations can be carried out using liquid media of suitable density and suitable wetting behavior. Quartz sand and other soil particles show densities around 2.5-3.4 g / cm ³ , while zinc dust has a density of 7.09 and Hg of 13.55 g / cm ³ . Depending on the mercury content, the zinc amalgams show a density between the two values of the pure elements. If liquid phases (this only applies to soil and dewatered sludge) with densities around 1.5-2.0 g / cm ³ (e.g. saline solution), the lighter soil particles can be removed at the top, while the sediment Hg in Enriched form of zinc amalgam. In a multi-stage process, amalgam and soil can finally be completely separated from one another (gold panning process). Stabilizers are usually added to certain sedimentation analyzes. A corresponding overview can be found in Patat-Kirchner, Internship in Technical Chemistry, 3rd edition, Verlag de Gruyter, Berlin 1975, p. 47). Suitable stabilizers are also added for better separation of soil particles and amalgams in the process according to the invention. The aim is to keep soil particles apart from the amalgams mentioned, if possible, or to float them. The choice of stabilizers / floatation aids depends on the type of soil.

Zinc amalgams form in the form of a powder when mixed equal parts of zinc and mercury in acidified water. According to Gmelins Handbuch der inorganic Chemie, Volume 34, Part A "Mercury", p. 1065, a dilute HCl or H ₂ SO ₄ solution can be used. The mercury input in concentrated aqueous ZnSO ₄ solution also leads to the formation of a solid amalgam. Soluble and insoluble mercury salts are also converted by zinc in an acidic medium with the formation of mercury-rich amalgams. In order to effect an even better deposition of the zinc amalgam, solid metal parts can, for. B. Zinc granules can be added. The respective composition by weight percent is determined by the respective reaction conditions.

The stability in almost neutral water of the formed Amalgams is sufficient to separate them from the rest To be able to carry out components of the suspension and not to saturate the process water with zinc ions.

The zinc amalgams also react in air and under water with oxygen only with extreme zinc excess (2.5% Hg) or in the case of liquid amalgams, if their surface is violently agitation is always renewed. In all other cases sufficient passivation occurs due to ZnO formation. The zinc amalgams are also against dilute acids generally persistent.

Nickel and cobalt salts can be in at a neutral pH Water in amalgams combined with the corresponding advantage len are transferred. This is the case with coin and precious metals in principle also possible, although the reaction in dilute acids must run off. Thus, if necessary other heavy metals by amalgamation and subsequent Removable sedimentation.  

The use of aluminum instead of or in addition to Zinc is recommended if the nature of the to cleaning soil, mud or water This is allowed because aluminum alone in the case of mercury through water with mercury salts and metallic mercury silver can be brought to amalgamation. Aluminum can also by shaking with mercury mechanically who reacted without additional energy input the. The zinc amalgams have compared to the aluminum amalgams but the advantage of greater stability against Zer settlement. Both amalgamation agents have the advantage to be inexpensive.

The possibility of amalgamy used according to the invention tion of mercury with the resulting Solids has been known for a long time and includes incl chemical works mentioned. With the problem of success separation of mercury from the soil since the 1970s, numerous scientists have increasing scope. There is an abundance of publications also to corresponding meetings etc., which are all possible Solutions of the type mentioned in the introduction include. Still is the successful and at the same time inexpensive, simple invent Solution according to the invention has not previously been proposed. Here at it is necessary to dig out the ground, however can because of the low expenditure on equipment, the prince protective measures in the form of Gas extraction and treatment facilities etc. on-site be worked so that transport costs are eliminated.

In the following the invention is based on a diagram (Figure) explained in more detail using the example of the removal of  Mercury from the ground an advantageous process scheme indicates.

• 1. The excavated soil is gently chopped up so far nert that the particle size of the primary particles (Hg part chen or the corresponding connecting particles) remains.
• 2. Coarse material (wood, stones and debris) are separated. Here for example, vibrating screens are suitable. The rough well is washed and can be deposited.
• 3. By adding a larger amount of suitable liquid phase (dilute hydrochloric acid, etc.) a suspension is obtained poses.
• 4. The separation of a fine fraction with a separation limit of about 40 µm leads to a significant reduction in the amount of soil to be cleaned. The separation can be inexpensive stig done in hydrocyclones. The detached and washed sand is practically free of pollutants.
• 5. The suspension is conditioned by addition of zinc powders, zinc granules, aluminum powders or Alloys of both, being diluted in the case of zinc Acids are added. The mercury compounds or metallic mercury are converted into sedimentable zinc or aluminum amalgam. For conditioning with Zn or Al powders become mechanical depassivation ultrasonic energy is coupled into the powder surfaces.  
• 6. The amalgam is used in the subsequent multi-stage sedi mentation obtained as a concentrate.
• 7. The decontaminated floor is z. B. by a Kombina tion of settling tanks and belt presses from the liquid phase separated. The decantate and filtrate is called Um running fluid in the circuit.
• 8. The one separated from the liquid and decontaminated Soil is deposited on the same property.

The crucial step in the process is conditioning, with which the mercury and / or the mercury compounds be converted into zinc or Alamalgam, which is then by means of known sedimentation technique from the soil suspension can be separated. Through the additional use of Surfactants such as amphoteric surfactants that are biodegradable and only be added to the suspension in very small amounts, can mainly organic contaminants from the amalgams be separated and suitable soil components by Flotation can be removed better than without aids.

To improve sedimentation, for example Stabilizers such as potassium citrate to achieve a stable Dispersion of other substances contained in the soil (except zinc amalgam) are added.

One can also add flotation chemicals to the bottom Ingredients float up for easier separation leave, leaving the amalgam on the ground.  

If, as in the case of zinc, dilute acids are added have to be recommended z. B. acetic acid or the environment friendly moor extract that you can slurry anyway the floor can use. For the rest, the Einwir dilute acid a slight hydrogen evolution lung, the advantageously dissolved mercury salt reduced to metallic mercury, which then Amalgam forms.

Claims (6)

1. Process for the separation of heavy metals, in particular in the form of mercury or compounds thereof, Nick el and cobalt salts or compounds thereof from the Soil, mud and water, in which the earth rich, the sludge and water in an aqueous suspension be transferred to the mercury or compounds here of, nickel and cobalt salts by amalgamation into one sedimentable form are transferred and then be separated. 2. The method according to claim 1, characterized, that the amalgamation by adding powders of zinc and aluminum or their alloys is caused. 3. The method according to claim 1 or 2, characterized, that during the amalgamation, ultrasound into the suspen sion is coupled. 4. The method according to any one of the preceding claims, characterized, that surfactants are added to the suspension.   5. The method according to any one of the preceding claims, characterized, that in the case of soil before making the soil suspension the coarse portion of the excavated soil with a grain size greater than about 40 microns is separated. 6. The method according to any one of the preceding claims, characterized, that the separation by a density sorting process, preferably sedimentation takes place.