Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
  • C22B7/006—Wet processes
• • C—CHEMISTRY; METALLURGY
  • C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
  • C11D—DETERGENT COMPOSITIONS; USE OF SINGLE SUBSTANCES AS DETERGENTS; SOAP OR SOAP-MAKING; RESIN SOAPS; RECOVERY OF GLYCEROL
  • C11D3/00—Other compounding ingredients of detergent compositions covered in group C11D1/00
  • C11D3/16—Organic compounds
  • C11D3/26—Organic compounds containing nitrogen
  • C11D3/33—Amino carboxylic acids
• • 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
  • C02F1/26—Treatment of water, waste water, or sewage by extraction
• • 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
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
  • C22B3/04—Extraction of metal compounds from ores or concentrates by wet processes by leaching
  • C22B3/16—Extraction of metal compounds from ores or concentrates by wet processes by leaching in organic solutions
  • C22B3/1608—Leaching with acyclic or carbocyclic agents
  • C22B3/1616—Leaching with acyclic or carbocyclic agents of a single type
  • C22B3/165—Leaching with acyclic or carbocyclic agents of a single type with organic acids
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
  • C22B3/20—Treatment or purification of solutions, e.g. obtained by leaching
  • C22B3/26—Treatment or purification of solutions, e.g. obtained by leaching by liquid-liquid extraction using organic compounds
  • C22B3/32—Carboxylic acids
• • 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
  • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
  • C02F1/5236—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents
• • 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
  • C02F2001/007—Processes including a sedimentation step
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2101/00—Nature of the contaminant
  • C02F2101/10—Inorganic compounds
  • C02F2101/20—Heavy metals or heavy metal compounds
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2303/00—Specific treatment goals
  • C02F2303/16—Regeneration of sorbents, filters
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/20—Recycling

Definitions

• This invention relates to processes and materials for separating heavy metals from substrates such as contaminated soil, sludges, sediments, and industrial residues.
• substrates such as contaminated soil, sludges, sediments, and industrial residues.
• the heavy metals can be recovered for industrial use or can be disposed of separately from the substrate.
• the invention relates to such processes wherein conduct of the process can reduce environmental and other pollution problems due to heavy metal loading without an associated increase or shift in environmental problems due to some other contaminant .
• the invention also relates to processes and materials particularly suitable for metal recovery.
• an aqueous solution containing a chelating agent is exposed to an environment (e.g., a waste material) containing a compound of one or more metals which can be chelated by that chelating agent, some or all of the metals will form a chelate with that chelating agent.
• an environment e.g., a waste material
• a compound of one or more metals which can be chelated by that chelating agent some or all of the metals will form a chelate with that chelating agent.
• a wide variety of chelating agents are known, for instance as reviewed by Chen et al at pages 1185 to 1197 of Can. J.Civ.Eng.Vol 22, 1995.
• the equilibrium complexation constants for the various chelating agents with the various metals indicates the relative affinity and stability of any particular chelate and, when there is competition between metals, which metals will be chelated in preference to others .
• chelating agents will preferentially chelate divalent metals such as calcium, magnesium and ferrous iron and are sometimes referred to as hardness complexing agents, while other chelating agents have a particular tendency to form a chelate with heavy metals such as copper, lead, cadmium, zinc, nickel or mercury.
• citric acid and NTA are commonly used as hardness complexing agents and EDTA is usually the material of choice for chelating heavy metals.
• EDTA is usually the material of choice for chelating heavy metals.
• a wide variety of other chelating agents that are discussed in the literature are various phosphates, phosphonates and various imino acids.
• Contamination of soils, sediments and municipal or industrial wastes by heavy metal pollutants is a major environmental problem. For instance there are areas of ground which are contaminated by industrial waste containing heavy metal such that there is a risk of the heavy metal getting into ground water or crops, and there are large volumes of river and sea sediments which are contaminated with toxic heavy metals .
• the article by Chen et al reports the screening of 190 chelating agents (including all those mentioned above) and examines in particular the performance of ADA (acetamido imino diacetic acid) , SCMC (amino carboxyalkyl thio proponoic acid) and PDA (pyridine dicarboxylic acid) but does not make any clear recommendations .
• ADA acetamido imino diacetic acid
• SCMC amino carboxyalkyl thio proponoic acid
• PDA pyridine dicarboxylic acid
• EDTA and other preferred chelating agents has the risk of the chelating agent subsequently causing further contamination of the environment, since they persist in the environment .
• An object of the invention is to provide processes and materials for enabling the efficient extraction of heavy metal from a substrate without associated further contamination due to the introduction of an environmentally persistent chelating agent.
• a further object of the invention is to provide processes and materials for separating heavy metals from a substrate under conditions so as to provide a heavy metal concentrate which has a sufficiently high concentration that either it can be used economically as a source of heavy metal or has relatively low volume such that storage or dumping in a controlled environment is economically and environmentally convenient.
• the invention provides a process for separating heavy metal from a water- immiscible substrate, wherein the process comprises extracting the metal from the substrate by contacting the substrate with an aqueous treatment solution containing active [S,S]-EDDS and thereby forming an extract solution of heavy metal chelate, separating the extract solution from the substrate, and then separating the heavy metal from the extract solution.
• EDDS is ethylene diamine disuccinic acid or ethylene di-imine butane dioic acid. It can exist in various optical isomeric forms .
• the form which must be used in the invention is the [S,S] form.
• active [S,S]-EDDS in the form of the ion, the free acid or the alkali metal salt or any other chemical form such that it is capable of acting as a chelating agent for heavy metals.
• the invention also includes materials suitable for use in such a process. Included amongst these materials is a composition comprising active [S,S]-EDDS and one or more materials selected from (1) microorganisms or enzymes for promoting release of heavy metal from the substrate, (2) biodegradable surfactant for promoting release of heavy metal from the substrate and/or emulsifying hydrophobic material from the substrate into the aqueous treatment solution, (3) biodegradable hardness chelating agent for preferentially chelating calcium and/or magnesium and/or ferrous metal from the substrate, (4) flotation, coagulation or flocculation agent, (5) acid, base or buffer for altering or controlling the pH of the substrate to a working optimum range, (6) oxidizing or reducing agents to facilitate release of the metals from certain fractions of the substrate, and (7) solvents.
• active [S,S]-EDDS active [S,S]-EDDS and one or more materials selected from (1) microorganisms or enzymes for promoting release of heavy metal from the substrate
• the [S,S]-EDDS is a powerful chelating agent for heavy- metals and is readily biodegradable in all environmental compartments by indigenous microorganisms . For instance it is rapidly and substantially completely degraded in a suitable environment within 28 days, and usually within 14 days or less in a batch test.
• the [S,R] and [R,R] isomers are not readily biodegradable according to EU and OECD regulations .
• the heavy metals are usually one or more of Cu, Cd, Hg, Zn, Pb, Ni and Cr.
• EDDS is included in the list of chelating agents in the article by Chen.
• the use of EDDS compounds as allegedly biodegradable chelating agents, and the existence of various isomers, and their synthesis, has been well known in the literature for many years, see for instance CAS abstract 65:11738F of 1966, CAS abstract 91(5):38875F of 1978, U.S. 3,158,635 and EP 267,653, with the production of [S,S]-EDDS being specifically described by Neal and Rose, Inorganic Chemistry, Volume 7, 1968, pages 2405 to 2412 "Stereospecific Oligins and their Complexes of EDDS".
• the [R,R] and [R,S]/[S,R] isomers are significantly less biodegradable than the [S,S] isomer and so preferably the EDDS used in the invention consists mainly or essentially only of [S,S]-EDDS. Generally therefore at least 80% by weight and preferably at least 95% by weight of total EDDS is in the [S,S]-EDDS form.
• the proportion of [S,S] isomer is as high as is reasonably practicably obtained by whatever synthetic method is being used (such as the method in Neal and Rose) and is preferably as close to 100% as is conveniently attainable.
• any other chelating agents are used in combination with the [S,S]-EDDS it is preferred that they should be biodegradable with the result that the amount of non- biodegradable chelating agent used in the processes of the invention is kept to a minimum, and is preferably less than 50%, and most preferably less than 20 or 10% by weight based on total chelating agent and preferably is zero or as near zero as is conveniently possible.
• EDDS refers to EDDS where the [S,S] form is predominant, as described hereinbefore.
• the process of the invention has the advantage that any of the chelating agent which escapes into the environment is biodegraded within a reasonably short time. Accordingly the process of the invention (unlike processes using materials such as EDTA) does not have the effect of introducing a long-term and undesirable pollutant into the environment .
• the substrate must be water immiscible and insoluble in the sense that it is possible to extract the heavy metal from the substrate by contacting the substrate with the aqueous treatment solution whilst avoiding dissolution of most or all of the substrate into the treatment solution. Generally little or no dissolution of the substrate occurs into the treatment solution.
• the substrate may be a water- immiscible liquid.
• it may be oil contaminated with zinc or other heavy metal.
• the substrate is a solid or semi-solid material, for instance as a slurry.
• the extraction step may be conducted in. situ or ex situ, that is to say it may be conducted where the substrate is initially located (jin situ) or in a mixing apparatus into which the substrate is transferred (ex situ) .
• Preferred jln situ contact processes comprise percolating the treatment solution through a bed of the substrate and collecting the extract solution from the bed.
• the percolation may be conducted under gravity or may be forced by pumping the solution through the bed, for instance substantially horizontally.
• Such processes are of particular value for treating contaminated soil since the treatment solution can be drained down through a permeable layer of the contaminated soil to collectors beneath the soil or can be pumped across a permeable layer of the soil, for instance from injection points immersed in the soil to collectors immersed in the soil at a lateral distance from the injection points.
• the invention is also of use when a stack has been formed of contaminated substrate in which event this stack can, for instance, be sprayed with the treatment solution and the extract solution can be drained off from the bottom of the stack.
• Examples include the recovery of heavy metal from stacks of municipal or industrial waste such as organic or inorganic discharges, and stacks of waste water sludge or other composting material.
• the invention it is possible to recover valuable metals from waste or dumps (or other mineral processing or mining wastes) and it is possible to remove the heavy metal pollution of composting material such as municipal waste or agricultural waste .
• Ex situ processes of the invention are generally conducted by mixing the treatment solution with the substrate in a mixing or scrubbing reactor or other apparatus. It is necessary for there to be sufficient duration of contact, having regard to the volume and time available, between the treatment solution and the substrate to achieve sufficient extraction of heavy metal from the substrate prior to final separation of the extract solution from the substrate. If there is insufficient extraction of heavy metal in a single pass, the process conveniently can be conducted with the extract solution being separated from the substrate and then recycled within or into the mixing apparatus as treatment solution for the next pass, and with the separation and recycling being conducted as many times as is required. Typically it may be recycled five to ten times or more.
• separation of the extract solution may be by any convenient technique. It can be assisted by flotation but is generally a liquid phase sedimentation process.
• the substrate When the substrate is a solid, it is normally a particulate solid which can conveniently be mixed with the treatment solution in the mixing apparatus which can be rotating drum or a stirred tank or scrubber system containing mixers such as paddles.
• the mixing apparatus may thus be, for instance, a simple tank provided with paddles or it may be a more complex arrangement of continuous flow mixers or a counter-current unit.
• the separation of the extract solution either after each pass or after the final or only passage through the apparatus, can be by any convenient solids liquid dewatering or separation process such as filtration, sedimentation, centrifugation or flotation.
• the ex situ processes of the invention are of particular value when applied to particulate solid materials such as industrially contaminated soil, river or harbour sediment, waste from a mineral mining or processing plant, cellulosic waste solids (for instance sludge or cake from mill waste or a deinking plant) , industrial waste sludge solids and municipal sewage sludge solids.
• the various sludge solids may be supplied to the process of the invention as a slurry or, for instance, more than 2% and often more than 10%, but usually less than 50%, solids in water or they may be supplied as a cake or even a relatively dry material.
• the invention is combined with the treatment of domestic or industrial waste water whereby, before dewatering the sludge produced in the treatment, the sludge is treated with the EDDS treatment solution so as to extract heavy metals.
• the treated sludge is dewatered in conventional manner, and the heavy metal is separated from the extract solution by any of the means described before.
• metal-contaminated soil, or river or harbour sediment is subjected to the extraction treatment of the invention.
• the substrate may first be separated in fractions to facilitate the process, after which all or only some of the fractions are treated further.
• the starting material is a mixture of sand with clay or silt
• hydrocyclon treatment or other process for separating the sand from the clay or silt will tend to leave a sand fraction having low heavy metal contamination and the silt or clay fraction having higher contamination. This fraction can then be subjected to the process of the invention.
• part or all of the substrate may initially be in a suspended form in which event it is desirable to bring it out of suspension as a coagulate or flocculate by treating the suspension with a coagulant or flocculant, thereby coagulating or flocculating the suspended material so as to form the substrate which can then be treated with the treatment solution in accordance with the invention.
• Enzymes, or microorganisms which will generate enzymes, which promote the release of heavy metal compounds from the organic fraction of the substrate can be included in the treatment solution.
• microorganisms or enzymes which will degrade humic or fatty acid, cellulosic, carbohydrate or other materials which will tend to hold the heavy metal compounds to the substrate may be incorporated in the solution.
• cellulase, lipase or amylase for this purpose. Suitable amounts are 10 to 500mg (usually as prilled material) per kg substrate.
• Surfactant can be included for the purpose of improving contact between the substrate and the treatment solution and/or for emulsifying emulsifiable residues which would otherwise tend to repel the treatment solution from the substrate or prevent or minimise wetting of the substrate by the treatment solution.
• an emulsifier may be used to promote emulsification of the immiscible liquid into water provided that it is possible subsequently to break the emulsion and separate the extract solution from the water-immiscible liquid.
• the surfactants should be rapidly and substantially completely biodegradable, by which we mean they should be biodegradable either under substantially the same conditions as are used for biodegrading the EDDS or such that they will biodegrade at a reasonable rate when the effluent from the process reaches the river or other final environment.
• the surfactant biodegrades at least 80% (and preferably 100% or close to 100%) under the conditions that result in substantially complete biodegradation of the EDDS during the process of the invention.
• the surfactant (or surfactant mixture) may be selected from materials that will sorb on to the substrate only to a very low extent .
• Suitable anionic surfactants for use in the invention include alkyl (usually C10-14) sulphates and ethoxylated alkyl sulphates (both of which are generally readily biodegradable anaerobically or aerobically) and linear alkyl benzene sulphonate when the biodegradation is aerobic and secondary alkane sulphonates .
• ethoxylated alkyl sulphates especially c 10-14 alkyl with 1 to 4 ethoxy groups, is particularly preferred, alone or in combination with other surfactants.
• Suitable non-ionic surfactants which can be used in the invention are ethoxylated fatty alcohols (especially c 10-14 alkyl with 7-15 ethoxy groups) , glucamides, and alkyl polyglycosides .
• Suitable surfactants which can be used in the invention include cationics.
• surfactants may be produced biologically, e.g., as in Applied and Environmental Microbiology, Oct 1992, p 3276 to 3282 and Water Environment Research, Volume 64 No .2 , March/April 1992, p 163 to 169.
• the total amount of surfactant which is included in the treatment solution is generally from 10 to 20000mg/l, preferably 10 to 5000mg/l, or lOOmg to lOOg, preferably lOOmg to 20g per kg substrate. The amount should be above the CMC.
• the EDDS is utilised primarily for chelating the environmentally troublesome heavy metals such as copper, cadmium, mercury, zinc and lead
• a hardness complexing agent which is preferably biodegradable, that is to say a chelant which is preferably substantially biodegradable under the same conditions as the EDDS (or after discharge) and which will preferentially chelate calcium and/or magnesium and/or ferrous iron.
• Typical hardness complexing agents include citric acid, fatty acids and NTA. Zeolite and phosphate can also be used. The amount may be lOOmg to 20g/kg substrate.
• Other materials which may be included comprise materials to facilitate subsequent separation of the substrate from the extract solution, such as flotation aids (when the separation is by flotation) or inorganic or polymeric coagulants when it is by coagulation or polymeric flocculants when it is by flocculation.
• compositions for use in the invention are single pack compositions which contain EDDS and one or more of (a) microorganisms or enzymes for promoting release of heavy metal, (b) biodegradable surfactant, (c) hardness complexing agent, (d) flotation or coagulant or flocculation aid, and (e) acid, base or buffer.
• the compositions may be in the form of solids but are often liquids, preferably concentrated liquids.
• EDDS typically contains 10-60% (often 10-30%) EDDS, 0-25% (often 5-15%) surfactant system which typically contains AES optionally with AE and/or AS, 5-40% (often 5-20%) hardness complexing agent, 0.2-5% (often 0.5-2%) enzyme, 0-20% other processing aids including e.g. solvents, peptizing polymers, pore blocking agents, balance water (all percentages being by weight) .
• the separation of the extract solution from the substrate can be conducted by known methods which are applicable when the chelating agent is some other material (such as EDTA) in place of the EDDS, such as the separation and recovery techniques proposed in the literature.
• the chelating agent is some other material (such as EDTA) in place of the EDDS, such as the separation and recovery techniques proposed in the literature.
• the separation of the heavy metal from the extract solution i.e., the solution which is obtained by treating the substrate with the EDDS-containing treatment solution
• the separation of the heavy metal from the extract solution can be conducted by a number of processes, preferably one of the following processes, or combinations thereof :
• the EDDS moieties of the heavy metal chelate in the extract solution are biodegraded thereby releasing the heavy metal from the chelate, and the released heavy metal is separated from the extract solution.
• the metal and the EDDS moieties of the heavy metal chelate are separated in the extract solution by means other than the biodegradation of EDDS, and the EDDS moieties and the heavy metal are separately recovered from the extract solution.
• Processes of the second embodiment have the advantage that they allow to remove EDDS which can then be reused, whereas processes of the first embodiment destroy the EDDS.
• processes according to the second embodiment can be combined, i.e. more than one of such means can be used in sequence, and processes according to the first and second embodiments can also be combined.
• the process according to the first embodiment is preferably used last, as a finishing step.
• the invention offers the additional advantage that the step of biodegradation can be used to degrade substantially all the chelating moieties within a reasonably short time (and often very rapidly) , thereby releasing the heavy metal from the chelate.
• the release of the heavy metal from the chelate then permits convenient and controlled separation of the released heavy metal from the extract solution.
• the biodegradation is either conducted aerobically or anaerobically .
• the extract solution will usually contain sufficient nutrient for effective conduct of the biodegradation but if necessary additional carbon source or other nutrient can be added to promote bacterial growth and the biodegradation process.
• the heavy metal which is released from the chelate in the extract solution during the biodegradation can be separated by ion exchange, electrolysis, or other techniques but preferably it is separated by precipitation.
• the precipitation may follow as a result of the formation of any suitable insoluble compound of the heavy metal, but generally the most convenient heavy metal compound to be formed as precipitate is the metal sulphide or metal hydroxide.
• the sulfide can be formed by bacterial reduction of elemental sulphur, sulphate or other oxidized sulphur sources.
• the conditions that prevail in an anaerobic digester will generally contain sufficient sulphide to cause spontaneous precipitation as heavy metal sulphide of the heavy metal which is released from the chelate by biodegradation.
• additional sulphide for instance bubbled as hydrogen sulphide, may be added to promote the desired precipitation.
• a sulphate may be added to generate sulphide in situ.
• the extract solution containing the chelate When the digestion is being conducted anaerobically, it is convenient to feed the extract solution containing the chelate, generally at a pH around 6 to 8, into an anaerobic digestion apparatus.
• the extract solution can be fed at the base of the reactor beneath a blanket of anaerobic sludge granules maintained at a temperature typically of 15°C-55°C, preferably 25°C-40°C.
• Additional nutrient for instance in the form of waste water, can also be fed into the reactor with the extract solution. If necessary, the feed may also include inoculum for initiating the biodegradation.
• methane is • generated (and may be utilised as a source of heat or other energy in the process) and water and solids containing metal sulphides (or other separated metal) can be removed continuously or intermittently .
• the digestion When the digestion is being conducted aerobically, it may be conducted in any suitable reactor such as in a mixed aerated tank at 7 to 30°C which contains an aqueous suspension of flocculated bacteria and into which the extract solution is pumped (i.e., an activated sludge system) , a biological aerated filter, a sandfilter, a trickling filter through a sand or stone bed with bacteria on the solid particles, or by a fluidised bed reactor.
• Additives may be added to the influent to stimulate and stabilize the reactor, such as e.g. phosphates, iron salts, flocculating agents, etc.
• the resultant solution, containing dissolved heavy metal compound, can then be passed through an ion exchanger to recover the heavy metal or can be subjected to precipitation, for instance under reduction with hydrogen sulphide, to form the sulphide precipitate, or as a hydroxyde .
• the heavy metal can, alternatively, be recovered by electrolytic precipitation from the extract solution after biodegradation .
• the heavy metal sulphide or other precipitate can then be recovered either as a relatively concentrated, for instance above 10% and often above 20 or even 50% dry weight aqueous suspension containing heavy metal compound and may, for instance, be recovered from the aqueous liquor by a liquid solids separation process such as filtration, sedimentation, or centrifugation, optionally followed by drying, and may thus be provided as a substantially dry cake or even a powder.
• a liquid solids separation process such as filtration, sedimentation, or centrifugation, optionally followed by drying, and may thus be provided as a substantially dry cake or even a powder.
• the process of the invention has the advantage that the heavy metal contamination is concentrated within a very small volume.
• the precipitated or otherwise separated heavy metal for an industrial process, for instance as a source of heavy metal for some industrial use.
• this second embodiment of the invention offers the advantage that the EDDS is not destroyed, and can therefore be reused.
• a first means involves exchanging heavy metals against sulphide.
• the extract solution is contacted with an excess of sulphide, preferably sodium sulphide, at a pH in the range of from 10 to 13. Under these pH conditions, sulphide has a higher affinity for heavy metals than EDDS does. Accordingly, metal sulphide complexes are formed on one hand, and free EDDS on the other hand.
• the metal sulphide complexes are insoluble and can be precipitated by any of the methods known to the skilled person. Precipitation of the metal sulphide complexes can be facilitated by the use of flocculating agents, such as calcium.
• an aqueous solution of EDDS is obtained which can be reused to treat another contaminated substrate; as an alternative, that solution can be acidified such that the EDDS is precipitated. This is particularly desirable to obtain more concentrated solutions of EDDS.
• a second means involves acidifying the extract solutions such that the interaction between the EDDS moieties and the heavy metals is weakened, then binding the heavy metal on a substrate having a higher affinity for heavy metals than EDDS in those acidified conditions.
• suitable substrates are well known to the skilled person, and include columns or beads of ion-binding resins such as are available in the DOWEX ® series, and as described in US
• an aqueous solution which comprises free EDDS.
• this solution can be reused, or EDDS can be precipitated therefrom.
• a third means involves contacting the extract solution with an electrolysis-cell.
• the extract solution is provided at the cathode, on which the metals are reduced and precipitate as a film.
• the resultant solution contains free EDDS.
• the cathode and the anode are separated by a membrane preventing the passage of EDDS to the anode, where it would otherwise be oxidized. As before, this solution can be reused, or EDDS can be precipitated therefrom.
• a sandy soil from a metallurgy site was mixed in a lab- scale slurry reactor containing a 50 mM [S, S] -EDDS-Na solution at pH 7-9.
• the slurry had a liquid/solid ratio of 5L/kg and was kept agitated on a rotary shaker (except otherwise noted) .
• the extent (%) of metal extraction from the solid phase was followed by measuring the metal concentration in the aqueous phase and dividing this value by the amount of metal initially present in the soil.
• the metal concentration in the aqueous phase was determined by flame atomic absorption spectrophotometry following solids removal (centrifugation) and total extraction (ashing and acid extraction) .
• Similar experiments were also carried out with harbour sediments and waste activated sludge (WAS) (a L/S ratio of 50, instead of 5, was used in the case of WAS) .
• WAS harbour sediments and waste activated sludge
• the table 1 illustrates the extent of metal extraction achieved with both the above procedure or with a more intensive extraction procedure involving high shear rate mixing (propeller-driven at 300 rpm) and the co-additon of various surfactants.
• [S,S] -EDDS-Cu, [S,S] -EDDS-Cd, or [S, S] -EDDS-Ni each at 10 mN in order to validate the recovery process under conditions of heavier pollution levels.
• Solid Ca(OH) 2 and Na 2 S were added at final concentration of 20 and 11 mM, respectively.
• the mixtures were left standing for two hours (pH 12.4), filtered (8 ⁇ m) and analyzed for [S,S]-EDDS and metals.
• the metal removal efficiencies are summarized in Table 3. All the [S,S]-EDDS remained in solution (as [S, S] -EDDS-Ca) which can therefore be re-used for the cleaning of another batch of soil or, alternatively, be acidified to pH 3-4 in order to recover
• the bioreactor used in this example was a Biological Aerated Filter (BAF) consisting in a lm high bed of porphyre stones (5-7 mm diam.) through which the spent extractant solution gravity-flowed counter-currently with air injected at the bottom.
• BAF Biological Aerated Filter
• the spent extractant was pumped to the top of the BAF column where a ponding depth of 30 cm was provided by raising the outlet pipe above the carrier bed.
• the hydraulic residence time was one day and the organic loading rate was 2-3g COD/d.L reactor solution (COD refers to the chemical oxygen demand) .
• the BAF columns were fed with spent extractant solutions which had, as described above, been amended with additional amounts of various [S, S] -EDDS-Me complexes (pH 7).
• the columns were inoculated with 1 L of activated sludge which had been adapted to [S, S] -EDDS-Na.
• Table 2 Efficiency of various processes for the removal of metals from ( [S, S] -EDDS-Me) -laden spent extract solutions .
• Separation modes b, b2 and b3 can be used alternatively or in any combination.
• Example 2 A Belgian metal-polluted river sediment was pretreated via sieving and hydrocyclone treatment to separate the fraction >55 ⁇ m. This sandy fraction was further decontaminated, with focus on the removal of heavy metals (several types of organic pollutants were equally present) .
• the treatment was executed in a scrubbing unit with slurry concentration of ca. 250g dry matter per litre water with acidification and chelator treatment at 20°C.
• the pH of the suspension was lowered from 6.7 to 5.0, in combination with the dosage of [S,S]-EDDS (5.5g/l) together with citrate (lg/1) and non- ionic surfactant (A12E09, lOOmg/1) .
• the mixture was allowed to equilibrate for 8h under continuous stirring, after which the pH was lowered further to 2.5 with sulfuric acid, and another 4 hours of contact time was allowed.
• the sediment was filtered and washed twice with demineralised water (100ml/250g slurry) .
• the extraction efficiency of this treatment is shown in Table 3 for the different metals.
• the acidic metal-containing effluent was neutralised with NaOH to pH 6.5 prior to biological metal-recovery.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Life Sciences & Earth Sciences (AREA)
• Organic Chemistry (AREA)
• Environmental & Geological Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Mechanical Engineering (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Manufacturing & Machinery (AREA)
• Geology (AREA)
• Hydrology & Water Resources (AREA)
• Geochemistry & Mineralogy (AREA)
• Water Supply & Treatment (AREA)
• Health & Medical Sciences (AREA)
• Wood Science & Technology (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Soil Sciences (AREA)
• Processing Of Solid Wastes (AREA)
• Removal Of Specific Substances (AREA)
• Solid-Sorbent Or Filter-Aiding Compositions (AREA)
• Water Treatment By Electricity Or Magnetism (AREA)
• Extraction Or Liquid Replacement (AREA)

Priority Applications (1)

Applications Claiming Priority (4)

Publications (1)

Family

ID=8230969

Family Applications (2)

Family Applications Before (1)

Country Status (8)

Families Citing this family (12)

Family Cites Families (5)

• 1997
  • 1997-01-21 EP EP19970870004 patent/EP0853986A1/de not_active Withdrawn
• 1998
  • 1998-01-09 AU AU58228/98A patent/AU737654B2/en not_active Ceased
  • 1998-01-09 WO PCT/US1998/000591 patent/WO1998031779A1/en not_active Ceased
  • 1998-01-09 KR KR10-1999-7006555A patent/KR100371823B1/ko not_active Expired - Fee Related
  • 1998-01-09 EP EP19980901790 patent/EP0972001A1/de not_active Withdrawn
  • 1998-01-09 CA CA 2277156 patent/CA2277156A1/en not_active Abandoned
  • 1998-01-09 NZ NZ50392698A patent/NZ503926A/xx unknown
  • 1998-01-09 JP JP53447098A patent/JP2001509734A/ja active Pending
  • 1998-01-14 ZA ZA98311A patent/ZA98311B/xx unknown

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events