HU185194B - Method for detoxication mixing tannery sewage sludges - Google Patents

Abstract

The invention relates to a method for detoxifying treatment and optionally for the recovery of toxic heavy metal complexes and organic sewage sludge containing industry, in particular the leather industry, in which the sewage sludge mixed with water to a maximum of 100kg / m high 3, preferably 20 to 40kg / homogenized, the resulting suspension with sulfuric acid or containing at least 30% sulfuric acid mineral acid mixture such that the acid concentration of the sludge suspension does not exceed 10Gew .-% and the pH of the suspension after completion the acid addition remains below 1, whereupon the acidified mixture is stirred at 20 degrees to 100 degrees C to decompose the heavy metal complexes, which separates the resulting acidic solution containing heavy metal salts from the slurry and expediently neutralized with lime. The metal salts are then precipitated at a pH of 8 to 10, and the separated sludge is freed from the heavy metal ions and acids by washing.

Description

The present invention relates to a process for the detoxification treatment and optionally utilization of toxic heavy metal salt complexes and organic materials, preferably dermatological sludges.

During tanning and dressing of hides, 80-95% water-containing sewage sludge is produced, which, due to its high organic content, can provide excellent plant nutrients, but the heavy metal ions - often significant chromium ions - used in manufacturing technology render them toxic.

Combustion of sludge is uneconomical due to its high water content. Many methods are known using various flocculating agents to compact and filter colloidal organic materials, but the economical dewatering of sewage sludge remains an unresolved problem.

High-moisture sewage sludge is usually deposited in reservoir ponds, but due to the toxic effects of heavy metal salts, the choice of landfill is increasingly problematic in addition to increasingly stringent environmental regulations.

No references or solutions have been found in the literature for extracting toxic materials from sludge and utilizing components.

It is an object of the present invention to provide a process for extracting the chromium and other heavy metal salt content of sewage sludge and converting residues containing organic matter into ever more environmentally friendly and even agriculturally useful forms. The invention is based on the discovery that heavy metals in the form of various organic and inorganic complexes and water-insoluble precipitates

- they are predominantly broken down by controlled hydrolysis of Cr ^{+ + +} compounds with a mineral mixture containing at least 30% sulfuric acid and removed from the sludge in a water-soluble form.

The process according to the invention comprises contacting the homogenized sludge with a maximum solids content of 100 kg / m ³ , preferably 20-40 kg / ιη ³ , with sulfuric acid, hydrochloric acid, nitric acid or phosphoric acid containing at least 30% sulfuric acid at 20-100 ° C. C, with vigorous stirring, so that the acid concentration in the suspension does not exceed 10% by weight during the addition and the pH of the solution drops below I after chemical reactions have occurred.

If the concentration of the suspension exceeds the indicated value, a stable foam may be formed upon acidification, which will significantly slow down the rate of the chemical reaction.

If the acid or acid mixture used for the decomposition of the complexes does not contain sulfuric acid, the subsequent separation, sedimentation and filtration of the suspension is much more difficult than in the presence of sulfuric acid.

The decomposition rate of the complexes is already satisfactory at room temperature, so that the reaction proceeds at a given temperature of the suspension, the operation does not require any heat, but of course increasing the temperature increases the reaction rate. After a temperature-dependent reaction time, the suspension content of the suspension is concentrated, e.g. The product is washed with water or dilute sulfuric acid in a planter or arparator, free of heavy metal ions, neutralized with lime milk and separated from the solution. The heavy metal salt content of the solution separated from the sludge is concentrated by precipitation and recycled to a poison cemetery or after purification and separation. A schematic diagram of the process is illustrated in Figure 1.

Example

Fermented leather factory sewage sludge is de-chromed with the following characteristics:

Dry matter content: 200 kg / m ³

Organic matter content: 100 kg / m ³

Chromium ion content: 12 kg / m ³

The sludge contains traces of zinc and cadmium ions; as well as significant amounts of iron and calcium ions.

The slurry to be processed is mixed with water in a 1: 6 volume ratio in the homogenizer 1 or with acidic water containing chromium ion from the washer separation system. The quasi-homogeneous slurry is fed into reactor 2 where 150 kg of 96% sulfuric acid is added to 1 m ^{3 of} sludge to be processed and a residence time of 60 minutes at the actual temperature of the slurry is maintained with vigorous stirring.

The solids content of the slurry is concentrated in the separator 3, from where the condensed sludge enters the washer separation system 4 and then into the neutralization-separator system 5, at the outlet of which the heavy metal-free sludge is neutralized with lime milk. From the washing system 4, the washing water is returned to the homogenizer 1. From the separator 3, the chromium-containing solution is introduced into the separator 6, where metal salts are precipitated by the addition of lime milk at a pH of 8 to 10. The heavy metal ions precipitate in the separator 7 is separated from the lime water.

Advantages of the process according to the invention:

- the solution solves the environmental problems associated with the sewage sludge from the tannery, eliminates the need to build reservoirs and eliminates the need to transport toxic sludge;

- enables the agricultural use of high organic sludge for soil improvement;

- allows the further recovery of the valuable materials contained therein by further processing the recovered heavy metal salt precipitate.

Claims (2)

1. A method for detoxifying toxic water-insoluble toxic heavy metals, preferably containing Cr ^{+ + +} - organic and inorganic complexes and organic materials, preferably in dermal sewage sludges 185,194, characterized in that the sewage sludge is homogenized with a water solids slurry having a solids content of up to 100, preferably 20-40 kg / m ', and then a mineral acid mixture containing sulfuric acid and / or at least 30% sulfuric acid is added to the slurry, the acid content should not exceed 10% by weight and the acidity of the mixture should be below pH I at the end of acidification, stirred vigorously at 20-100 ° C for a time depending on the temperature, and the complex is decomposed; the solution is neutralized, preferably with lime milk, and the metal salts are separated at pH 8-10, washed by washing, and the organic sludge is washed with metal ion and acid free. 2. The process of claim 1 wherein the acidic washings are recycled to form a slurry.