Resources and Conservation最新文献

In eddy-current separation, forces are exerted on non-ferrous metal particles to separate these metals from solid material mixtures. These forces depend on the magnetic field inducing the eddy currents as well as on the electric conductivity and the shapes and sizes of the particles.

The present paper provides model calculations of the forces exerted in a vertical eddy-current separator. A quality factor was developed by which the magnetic configuration of these systems can be optimized. The quality factor was also used to design rotating disc separators.

In both separation systems the magnetic fields are produced by permanent magnets.

The validity of the model calculations was tested by measurement of the exerted forces.

Denmark has been one of the pioneers in waste recycling, through legislation and government subsidies and a unique combination of private and public participation. This paper outlines major Danish activities in this field through 1982: government regulation, research and development, demonstration projects, community recycling centers, industrial activities, etc. In spite of these activities and a great deal of progress, it appears that only the surface has been scratched, and that steps should be taken to give further opportunity for recycling.

Only some of the papers presented at the seminar are included; a few on central sorting, modelling of waste recyc;ing, and economic incentives for recycling could not be finalised in time for this issue. It is hoped that these will be published in the near future.

There is no doubt that waste management will continue to grow in importance and cost throughout the world. Interest in energy as a recovered product is believed to be short term, as there is perceived to be greater potential benefit in recycling materials. Technology is not a limiting factor in implementing recyling activities, but it is economics that will determine what is acceptable; including direct processing costs and indirect environmental costs and benefits.

Ammoniacal ammonium chloride etchants are widely used to etch copper during the manufacture of printed circuit board (PCBs). Etching efficiency declines above 110 to 130 g/L copper and this concentration must be restored once the concentration reaches 150 to 170 g/L copper. The annual European arising of spent etchant (about half the U.S.A. arising) is estimated to contain 2250 Mg copper. Disposal of spent etchant involves a loss of resources and is usually environmentally unacceptable. This paper reviews methods for the regeneration of spent etchants with co-recovery of a saleable copper product. Whilst large volume flows of spent etchant are regenerated commercially, there is a need for methods appropriate to on-site treatment by the smaller PCB producer. Experimental developments designed to meet this need, using either supported liquid membranes impregnated with a diketone extractant or an electrochemical cell divided by solid ion exchange membrane, are described. The performance of the ion exchange membranes tested in the membrane cell was found to be inadequate for this application. It is concluded that a supported liquid membrane process, after further development, in combination with copper electrowinning from an acidic solution may fulfil the need for on-site treatment by the smaller PCB producer.

RIM-NUT, a new physico-chemical process for ammonia and phosphate removal from municipal secondary effluent by selective ion exchange, and precipitation of MgNH₄PO₄ slow-release fertilizer, has been tested in a 10 m³/h demonstration plant at West Bari Sanitation Station.

The three-month demonstration indicated the technical feasibility of the process to meet the stringent Italian concentration limits for N and P discharge, as well as to recover quantitatively nutrient species in the form of premium-quality fertilizer (N:P₂O₅:MgO=4:26:16), almost sterile with a tolerable concentration of heavy metals.