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Caustic soda recovery system from aluminum extrusion processes


“AKSODA-RE”: Caustic soda recovery system from aluminum extrusion processes


“AKSODA-RE” is an engineered system designed to recover soda from solution spends at the aluminium dyeing moulds. Used soda is recovered to a minimum of 85% in very pure condition (5gr/lts aluminium).
The caustic soda recovery system “AKSODA-RE” works continuously and automatically and this allows obtaining always the same concentration of the caustic soda solution. The system design is a closed loop: no caustic soda consumption, no toxic waste disposal of spent soda solutions, same quantity of aluminium on the plant processes, same quantity of aluminium extracted from the processes in form of alumina trihydrate sludge.
The system includes all the required equipment to be ready for use and simple installation and an integrated intelligent automatic and electronic control panel for monitoring and operating diagnostics alarms.
The system is mainly constructed from corrosion resistance materials to compact the extreme harsh process environment in order to insure long term life and service.
By using the “AKSODA-RE” system for soda recovery, the mill’s toxic/hazardous liquid wastes are minimized and at the same time save acid for pH equalizing, no conductivity at dangerous limit levels presents to the effluents, less sludge forming, no handling costs required and the raw soda ash drop down to minimum levels. The standard version includes the treatment of the evaporated alkaline solutions, for human and environment protection.

Parts of the system
  1. Soda solutions collection
  2. Reactor feeding
  3. Chemical clarification on reactor
  4. Membrane filtration
  5. Recovered soda recycling
  6. Fumes removal
  7. “AKDRY” - Indirect heating Sludge dryer
  8. Dry sludge filling unit
System description

Bath’s spend caustic soda solutions are collected to a receiver tank (BRT), where a pump recirculates bulk to avoid precipitation and help temperature homogeneity. Temperature and level at the tank are monitored for automatic and remote control.
A steady flow chamber (SFC) helps pump’s (CFP) suction control fro transferring a specific volume of liquid to the soda clarification reactor (SCR).
The clarification is based on catalytic crystals forming. The catalyst is an inorganic complex agent, special formulated to start and accelerate aluminium oxides crystallization. It is added in very low quantities <1.5% of the waste aluminium, by an automatic dosing system (ADS).
During reaction process an air-pump (BWL) recirculates sediment from reactors bottom to achieve better reaction conditions.
Temperature is a critical parameter so must be controlled via an analogue transmitter (TMT). In case of low ambient temperatures the reactor solution must be heated. To do that, immerse heating resistances are adapted at reactors side walls.
At the end of reaction time, the aluminium oxides crystals that have formed flocculates are separated from caustic soda solution as sediment at reactors bottom.
The clarified soda solution is then purified at a special membranes system (MBR) and stored to a tank (SRS) equipped with level and temperature sensors.
Finally, preheating via immersed heating resistances at storage tank and further concentration with new soda flakes or pellets, made recovered soda solution ready to be used at aluminium mould’s detachment process.
The aluminium oxide sediment from the reactor’s bottom is pumped (DFP) to an indirect batch dryer (SDF) for volume reduction and the dry material is packed to easily disposable big-bags at the filling system (SBP).
Vapours during drying and the vapours from bath or tanks containing soda solution in temperature above 80oC are being condensate at a barometric condenser, while the condensate liquid are disposed of with a perforated pipeline system to the land field.