Minimisation and utilisation of waste mineral sludge from sodium perborate production

Various approaches to waste minimisation, waste treatment and recycling or safe disposal of the waste mineral sludge from sodium perborate production are presented and critically discussed. Some most promising actions for waste (or its harmful potential) reduction on the production level are identified. These include: a) use of better raw materials (richer boron ore), b) improvement of the ore leaching process, and c) intensification of sludge washing and dewatering. These source reduction measures have already resulted in 50% reduction of boron content in the sludge. Utilisation of the raw or treated (e.g. dried, compacted) waste sludge could be found in agriculture, civil engineering and construction material production. Agricultural use (as a lime substitute) is based on favourable content of calcium-magnesium minerals and alkali pH value of the sludge, and simultaneous absence of heavy metals. Application in civil engineering (as an aggregate) is possible after calcination, which is costly, or as a cement kiln additive. Stabilisation of sludge before disposal, when no utilisation is available, is possible by small addition of commercial binders (e.g. Portland cement) or larger amounts of pozzolanic wastes (e.g. coal fly ash).