Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
  • B01D61/42—Electrodialysis; Electro-osmosis ; Electro-ultrafiltration; Membrane capacitive deionization
  • B01D61/44—Ion-selective electrodialysis
  • B01D61/445—Ion-selective electrodialysis with bipolar membranes; Water splitting
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
  • C01F7/00—Compounds of aluminium
  • C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
  • C01F7/46—Purification of aluminium oxide, aluminium hydroxide or aluminates
  • C01F7/47—Purification of aluminium oxide, aluminium hydroxide or aluminates of aluminates, e.g. removal of compounds of Si, Fe, Ga or of organic compounds from Bayer process liquors
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
  • C01F7/00—Compounds of aluminium
  • C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
  • C01F7/46—Purification of aluminium oxide, aluminium hydroxide or aluminates
  • C01F7/47—Purification of aluminium oxide, aluminium hydroxide or aluminates of aluminates, e.g. removal of compounds of Si, Fe, Ga or of organic compounds from Bayer process liquors
  • C01F7/473—Removal of organic compounds, e.g. sodium oxalate

Definitions

• the invention relates to a process for reducing the dissolved inorganic and organic impurities in aqueous alkalis in the Bayer process for the production of aluminum hydroxide.
• the raw materials used in the Bayer process essentially bauxite and caustic soda, contain organic and inorganic undesirable substances which are introduced into the Bayer process in particular during the dissolution of the bauxite and subsequently in a variety of ways affect this adversely.
• the substances are acidic compounds such as Chlorides, phosphates, sulfates, vanadates, fluorides and / or organic salts or acids, in particular oxalates and humic acids.
• the impurities accumulate at various points up to critical values, provided they are not removed from the process.
• Process-related as well as economic problems are associated with the impurities. Cumulatively enriched, since they are obtained in the form of sodium salts, they lead to a reduction in the causticity and the proportion of free lye, which has the consequence that the lye productivity and thus the process economy decrease.
• the process control is hindered by deposits of the undesirable substances on tanks, pipes, heat exchangers and other devices, so that cleaning steps have to be carried out in order to restore the intended production output. Under certain circumstances, the cleaning steps can be quite complex, for example by rinsing acid must be carried out when the deposits reach layer thicknesses that can only be removed inadequately by mechanical means or the deposits are in inadequate places.
• the process economy is further reduced by the impurities in that they increase the alkali viscosity and thus the pump costs increase.
• the settling process of the hydroxide and its separation is negatively influenced.
• the inventors have therefore set themselves the task of presenting a process which is suitable for economically reducing the inorganic and organic dissolved impurities in aqueous alkalis in the Bayer process for the production of aluminum hydroxide and their concentrations in such a manner to keep low limits that they have practically no influence on the Bayer process.
• the object is achieved by a process in which the lye of an electrodialysis using at least one anion-selective and / or at least one cation-permeable membrane and at least one bipolar, water-dissociating membrane to form an alkali lye component, which is the Circulation liquor of the Bayer process is added and subjected to an impurity component which is removed from the process and discarded.
• the contamination level nente essentially contains the anionic acid residues of the contaminants from the contaminated alkali.
• the invention is based on the use of a bipolar membrane in the electrodialysis of the alkali metal hydroxide solution from the Bayer process.
• the generally written reaction takes place
• MX + H2O HX + MOH, where M is alkali and X is the acid residue.
• the salt thus forms as impurity and water, which is dissociated by the bipolar electrode.
• Alkali alkali and the corresponding acid, by the in the corresponding Ze . II areas react by the selective membranes enriched cations or anions with the dissociation products of the water. For example, the following reactions can take place individually or simultaneously:
• FIG. 1 the division of a contaminated lye stream in a cleaned caustic solution and a stream with impurities
• FIGS. 2 to 6 different arrangements of electrodialysis cells
• FIG. 7 the use of the electrodialysis cell (s) in the Bayer process cycle.
• the alkali lye stream P v loaded with impurities and originating from the Bayer process is electrodialysis using at least one anion and / or at least one cation permeable membrane and at least one bipolar membrane to dissociate the water qualified membrane subjected.
• a lye stream P r which is depleted of impurities and a separate current V which contains the impurities are obtained.
• FIGS. 2 to 6 show examples of possible arrangements of electrodialysis units according to the invention. Furthermore, arrows indicate by way of example and schematically in which cell areas the contaminated alkali hydroxide solution P v can be introduced and from which cell areas corresponding reaction products P r , V can be taken or where the / the current (s) of the cleaned ones Alkali P r and the current (s) of the impurities V occur.
• FIG. 7 shows in a highly simplified version the circulation of the lye in the Bayer process and the use of electrodialysis E-
• electrodialysis can also be used in other places of the circulatory process.
• the aforementioned locations are particularly preferred, since the necessary equipment can be installed at these points without significant operational changes and, on the other hand, the lye to be cleaned is diluted, which benefits the life of the membranes.

Landscapes

• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Health & Medical Sciences (AREA)
• Geology (AREA)
• Life Sciences & Earth Sciences (AREA)
• Inorganic Chemistry (AREA)
• General Health & Medical Sciences (AREA)
• Engineering & Computer Science (AREA)
• Water Supply & Treatment (AREA)
• Urology & Nephrology (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Separation Using Semi-Permeable Membranes (AREA)
• Water Treatment By Electricity Or Magnetism (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Applications Claiming Priority (2)

Publications (1)

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ID=4211189

Family Applications (1)

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• 1988
  • 1988-03-31 GR GR880100210A patent/GR880100210A/el unknown
  • 1988-04-11 EP EP88902782A patent/EP0309509A1/de not_active Withdrawn
  • 1988-04-11 BR BR888806904A patent/BR8806904A/pt unknown
  • 1988-04-11 HU HU882861A patent/HUT52005A/hu unknown
  • 1988-04-11 AU AU15433/88A patent/AU610158B2/en not_active Ceased
  • 1988-04-11 WO PCT/CH1988/000076 patent/WO1988007975A1/de not_active Application Discontinuation
  • 1988-04-13 ES ES8801134A patent/ES2006407A6/es not_active Expired
  • 1988-04-15 CN CN198888102321A patent/CN88102321A/zh active Pending

Non-Patent Citations (1)

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