Classifications

• • A—HUMAN NECESSITIES
  • A62—LIFE-SAVING; FIRE-FIGHTING
  • A62D—CHEMICAL MEANS FOR EXTINGUISHING FIRES OR FOR COMBATING OR PROTECTING AGAINST HARMFUL CHEMICAL AGENTS; CHEMICAL MATERIALS FOR USE IN BREATHING APPARATUS
  • A62D3/00—Processes for making harmful chemical substances harmless or less harmful, by effecting a chemical change in the substances
  • A62D3/30—Processes for making harmful chemical substances harmless or less harmful, by effecting a chemical change in the substances by reacting with chemical agents
  • A62D3/33—Processes for making harmful chemical substances harmless or less harmful, by effecting a chemical change in the substances by reacting with chemical agents by chemical fixing the harmful substance, e.g. by chelation or complexation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
  • B09C—RECLAMATION OF CONTAMINATED SOIL
  • B09C1/00—Reclamation of contaminated soil
  • B09C1/02—Extraction using liquids, e.g. washing, leaching, flotation
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/68—Treatment of water, waste water, or sewage by addition of specified substances, e.g. trace elements, for ameliorating potable water
  • C02F1/683—Treatment of water, waste water, or sewage by addition of specified substances, e.g. trace elements, for ameliorating potable water by addition of complex-forming compounds
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F11/00—Treatment of sludge; Devices therefor
  • C02F11/004—Sludge detoxification
• • A—HUMAN NECESSITIES
  • A62—LIFE-SAVING; FIRE-FIGHTING
  • A62D—CHEMICAL MEANS FOR EXTINGUISHING FIRES OR FOR COMBATING OR PROTECTING AGAINST HARMFUL CHEMICAL AGENTS; CHEMICAL MATERIALS FOR USE IN BREATHING APPARATUS
  • A62D2101/00—Harmful chemical substances made harmless, or less harmful, by effecting chemical change
  • A62D2101/40—Inorganic substances
  • A62D2101/43—Inorganic substances containing heavy metals, in the bonded or free state
• • A—HUMAN NECESSITIES
  • A62—LIFE-SAVING; FIRE-FIGHTING
  • A62D—CHEMICAL MEANS FOR EXTINGUISHING FIRES OR FOR COMBATING OR PROTECTING AGAINST HARMFUL CHEMICAL AGENTS; CHEMICAL MATERIALS FOR USE IN BREATHING APPARATUS
  • A62D2203/00—Aspects of processes for making harmful chemical substances harmless, or less harmful, by effecting chemical change in the substances
  • A62D2203/02—Combined processes involving two or more distinct steps covered by groups A62D3/10 - A62D3/40

Definitions

• the present invention relates to a method of removing heavy metals from soil, sludge, compost and similar materials.
• a known method of removing heavy metals from soil, sludge or compost comprises extracting the heavy metals with acid.
• the method suffers from the drawback that the heavy metal containing extract constitutes a problem of almost the same magnitude as the heavy metal containing material itself as the extract must either be disposed of by depositing, which is expensive and causes environ ⁇ mental problems or by processing at a special chemical reception plant which would in most cases also be too expensive.
• a further drawback of the known method is that in extraction of sludge a very low pH value is often required as the heavy metals are present in a strongly bonded state in the dead cells in the sludge. Consequently, large amounts of acid and base are required to lower and readjust, respectively, the pH value.
• the object of the present invention is to provide a method of removing heavy metals from soil, sludge, compost and similar mate ⁇ rials, whereby the heavy metals are concentrated to a larger extent than is the case in connection with the known methods.
• This object is obtained according to the invention by a method which is characterized in that the heavy metal containing material is treated with an agent forming a complex with heavy metal ions so as to form a product consisting of a solid phase and a liquid phase containing a heavy metal complex, in that the liquid phase is separated off, in that the liquid phase separated off is treated with an ion exchanger so as to bond heavy metals onto the ion exchanger, and in that the heavy metals are optionally removed from the ion exchanger by eluation.
• the heavy metal containing material is treated with a solid complex bonding agent in order to avoid an increase of the volume of the treated material. If the starting material is too dry the complex bonding agent is added as an aqueous solution.
• the pH value of the mixture of the heavy metal containing material and the complex bonding agent should preferably be in the range of about 3 to 5.5 and if necessary an adjustment of the pH value is carried out by using e.g. nitrous acid or sulphuric acid. However, the starting material will often have a pH value of about 5.
• the complex bonding agent may advan ⁇ tageously be added in solid form before the dewatering.
• the treatment with the complex bonding agent may optionally be repeated one or more times in order to obtain a desired degree of removal of heavy metals.
• EDTA or a mixture of EDTA and pyrophosphate is preferably used as complex bonding agent.
• EDTA as a complex bonding agent it is preferably used in a concentration of from about 5 to about 50 mmol per litre of heavy metal containing material.
• pyrophosphate it is preferably used in a concentration in the range of about 1 to about 50 mmol per litre of heavy metal containing material.
• the solid matter is separated from the liquid, which separation may be carried out by e.g. sedimentation, centrifugation or filtration.
• an ion exchanger based on bark is used, such as a sulphonated bark ion exchanger, as such ion exchangers are inexpensive.
• a sulphonated bark ion exchanger is capable of specifically absorbing about 0.3 equivalent heavy metal per litre. By “specifically” is meant that the absorption can take place without the influence of other ions possibly present, such as sodium ions and calcium ions.
• the overall capacity of the bark ion exchanger corresponds to about 1 equivalent per litre, but only about 30% of the ionic groups of the ion exchanger are specific to the absorption of heavy metals.
• the duration of the treatment on the ion exchanger is preferably in the range of about 30 to about 120 minutes.
• the collected heavy metals may optionally be eluted from the ion exchanger by e.g. acid so as to obtain the heavy metals.
• the bark ion exchanger may be burnt using an exhaust gas filter whereby the heavy metals are further concentrated in the ashes.
• the heavy metal containing material Prior to the treatment with the complex bonding agent the heavy metal containing material may be aired, whereby a considerably improved extraction of the heavy metals from the heavy metal con ⁇ taining material is obtained.
• the further treatment of the extract on an inexpensive bark ion exchanger in addition to the above discussed substantial concentration provides the advantage that the problem of the expensive treatment or depositing of the environmen ⁇ tally harmful extract is avoided and that the liquid used for the extractions may be regenerated and recycled, whereby the expenses for chemicals for the extraction are reduced considerably.
• 1 kg matured compost (wet basis) was aired for 30 minutes, and 20 mmol EDTA, 5 mmol pyrophosphate and 100 ml water were then added to reduce the content of dry matter to 60 % by weight.
• the compost contained 105 ppm lead and 4 ppm cadmium (wet basis), which it was desired to reduce to 40 ppm lead and 1 ppm cadmium (dry matter basis). After 15 minutes a pH value of 5.0 was measured.
• the 210 ml of extract were then treated on a sulphonated bark ion exchange column having a total volume of 100 ml.
• the period of treatment was about 2 hours the calculated residence time in the column being about 1 hour.
• the concentration of the extract of 52 ppm lead and 1.7 ppm cadmium was reduced to 1 ppm lead and 0.02 ppm cadmium by the treatment.
• the harbour sludge contained 2100 ppm lead, 41 ppm cadmium, 760 ppm chromium and 1450 ppm copper on a dry matter basis, and after the extraction it contained 235 ppm lead, 17 ppm cadmium, 184 ppm chromium and 210 ppm copper.
• the extract was treated on a 200 ml bark ion exchange column having a residence time of 45 minutes, whereby the heavy metal content of the extract was reduced to 12 ppm lead, 2 ppm cadmium, 12 ppm chromium and 2 ppm copper.
• the bark ion exchanger was saturated by treatment with a total of 8 times 1.2 kg harbour sludge correspond ⁇ ing to a concentration of 48 times.
• the extract which contained 208 ppm lead, was treated on a 100 ml bark ion exchange column having a residence time of 1 hour.
• a liquid having the same heavy metal concentration as the extract it was determined that a total of 60 soil samples of 200 g each can be treated on the ion exchange column before it shows any sign of saturation. This corresponds to a concentration of 120 times.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Environmental & Geological Engineering (AREA)
• Life Sciences & Earth Sciences (AREA)
• Organic Chemistry (AREA)
• Health & Medical Sciences (AREA)
• Hydrology & Water Resources (AREA)
• Water Supply & Treatment (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Health & Medical Sciences (AREA)
• Toxicology (AREA)
• Medicinal Chemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Business, Economics & Management (AREA)
• Emergency Management (AREA)
• Soil Sciences (AREA)
• Processing Of Solid Wastes (AREA)
• Treatment Of Water By Ion Exchange (AREA)
• Treatment Of Sludge (AREA)

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• 1989
  • 1989-11-07 DK DK553889A patent/DK553889A/da not_active Application Discontinuation
• 1990
  • 1990-11-07 EP EP19900916713 patent/EP0500657A1/de not_active Withdrawn
  • 1990-11-07 WO PCT/DK1990/000283 patent/WO1991006343A1/en not_active Ceased

Non-Patent Citations (1)

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