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
  • C22B26/00—Obtaining alkali, alkaline earth metals or magnesium
  • C22B26/10—Obtaining alkali metals

Definitions

• the present invention relates to a process for the separation of sodium and calcium from sodium sludge and, in particular, to the separation of sodium and calcium from the sludge produced as a waste product in the production of sodium by the electrolysis of a fused mixture of sodium chloride and calcium chloride.
• the sludge produced in the above process generally has a composition comprising 70% Na, 20% Ca and 10% mixed oxides but mainly Na2O. Currently, only sodium is separated and recycled and the calcium is not recovered.
• the present invention provides a process for the separation of sodium from a sludge containing sodium, calcium and oxides thereof which comprises the step of subjecting the sludge to a centrifugal force to separate the sodium from the calcium.
• the sludge is preferably restrained in a gauze cage made from a material which is not attacked by the sludge, for example stainless steel.
• the gauze may have a mesh size of from 25 to about 200 micrometres, preferably 25 to 125 micrometres.
• the gauze cage containing the sludge is preferably immersed in an oil bath maintained at an elevated temperature and preferably at a temperature in the range of from 110° to 200°C.
• the liquid used for heating can be any liquid that is non reactive with the sludge over the said temperature range, for example, mineral oils, kerosene (deodorised or otherwise) and liquid paraffin (light and heavy fractions).
• the gauze cage assembly can be preheated to the working temperature prior to loading with the sludge.
• the gauze cage may be rotated at a rate of up to 30,000 r.p.m., preferably 600 to 3,000 r.p.m., more preferably 2,000 to 3,000 r.p.m., in order to cause the sodium to separate from the calcium.
• the centrifugal force applied to the sludge causes the sodium to migrate to the edge of the gauze cage and to be flung through the gauze as a plurality of discrete particles which collect at the bottom of the oil bath.
• the centrifugal separation may be carried out under an atmosphere of an inert gas, for example, nitrogen.
• the sludge treated according to the process of the invention is preferably a sludge containing 70% sodium, 20% calcium and up to 10% of sodium oxide.
• particles of an inert material may be added to the sludge.
• the particles may be of a regular or irregular shape and may be, for example, glass beads or irregularly shaped glass particles, ball bearings, polymer beads or ceramic particles.
• the residue remaining after the separation of the sodium from the sludge may, if desired, be treated by one of the following methods to separate the calcium therefrom:
• a sludge was prepared for experimental purposes having a nominal composition of 70%Na, 20%Ca and 10%Na2O.
• the constituents of the sludge were heated to about 200°C in order to form a substantially homogeneous product.
• Separation of the sludge was carried out by placing the sludge in a stainless steel gauze cage having a mesh size of 125 micrometres.
• the cage containing the sludge was placed in an oil bath maintained at a temperature of 140°C and rotated at a speed of 1,500 r.p.m.
• the sodium was found to separate readily from the sludge.
• the calcium content of the sodium recovered from the sludge was found on an average of three analyses to be 0.044%.
• 1,3-Dibromopropane has a density of 1.9 g/cm3 which is between the density of calcium (1.55 g/cm3) and that of sodium oxide (>2.0 g/cm3).
• a sludge produced as a by-product of the Downs Cell electrolytic sodium production process was used in carrying out trials of separation.
• the composition of this sludge was nominally 70% Na, 20% Ca and 10% oxides, mainly Na2O.
• the sludge was placed into a stainless steel gauze cage with a mesh size of 125 micrometres and spun in hot mineral oil at 140°C. Thereafter, centrifugal separation at 3000 rpm was used for up to 3 minutes. The sodium separated from the sludge as discrete droplets through the mesh whilst the calcium and the oxide remained contained within.
• Example 2 The procedure of Example 2 was repeated, except that the mineral oil was replaced by a liquid paraffin heavy fraction having a density of 0.86 to 0.89 g/cm3 maintained at 150°C.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Geology (AREA)
• Life Sciences & Earth Sciences (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Manufacturing & Machinery (AREA)
• Environmental & Geological Engineering (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Centrifugal Separators (AREA)
• Treatment Of Sludge (AREA)
• Manufacture And Refinement Of Metals (AREA)

Applications Claiming Priority (2)

Publications (1)

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Citations (5)

• 1988
  • 1988-04-20 GB GB888809355A patent/GB8809355D0/en active Pending
• 1989
  • 1989-04-12 EP EP89303609A patent/EP0338719A1/fr not_active Withdrawn
  • 1989-04-20 JP JP9901189A patent/JPH0215132A/ja active Pending

Patent Citations (5)

Non-Patent Citations (1)

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