05 February 1994 00:00 [Source: ICB]
UK WASTE specialist Lanstar has developed a process to handle water-reactive wastes mixed with solvents at its Cadishead site near Manchester. It has just completed construction of a commercial plant which, with associated works, represents an investment of £400 000 ($590 000).
Initially the plant will be used to treat antimony pentachloride mixed with chlorinated and fluorinated solvents, arising as waste catalyst from ICI's CFC and CFC-alternatives production in the UK. Until now there has been no satisfactory disposal route for this reactive waste. ICI produces some 40 tonne/year of the spent catalyst and has three years' waste in store in special 12 tonne containers.
Dr John Parker, director and general manager of Lanstar's waste treatment division, describes the plant as highly versatile, and says it will be used for other wastes in the future as the ICI backlog is worked off, which could take up to 12 months, as the unit is charged with 600kg of waste per batch.
The Sb2O5/solvent waste is first hydrolysed by passing it into water in the sealed PTFE-lined reactor. Parker describes the hydrolysis stage as the most critical given the reactive nature of the waste. To ensure no contact with moisture in the air, the waste is transferred directly from the ISO container under a nitrogen blanket.
HCl offgases are trapped in a scrubber. The solution is then neutralised with caustic soda and antimony oxide/hydroxide precipitated into a slurry. After reaction, the bulk of the solvent is removed from the reactor vessel by steam distillation and the resulting water/solvent mix allowed to separate out - the solvent is blended with other hydrocarbon wastes and can be used for cement kiln firing.
The slurry is dewatered on a filter press. The filtrate from the dewatering and the water-phase separated from the distillation condensate are then treated with activated carbon to remove the last traces of halogenated solvents. The solvents and the spent activated carbon are finally destroyed off-site by high temperature incineration.
Lanstar is currently investigating the possibility of recovering and recycling the antimony from the filter cake, which contains some 45-50% as antimony hydroxide, the balance being moisture. Even though this would have to be paid for, says Parker, it would be more preferable than landfilling the waste.
The versatile nature of the plant means that in addition to hydrolysis it can be used for neutralisation, steam distillation, dewatering and activated carbon treatment of waste waters. Lanstar is planning, for example, to use the plant to recover solvents from aqueous mixtures.
Development of the process and financial investment has been assisted by ICI, explains Parker, who adds that 'more and more companies are demanding specialist treatment processes' to dispose of waste. The option in ICI's case would have been to export the spent catalyst for treatment. Lanstar has already approached other CFC and alternatives producers and has received interest in the facility from companies such as DuPont and Atochem.
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