Guidance Document for Management of Wastes from the Base Metals Smelting Sector

7.1 Minimization of Wastes and Residues
7.1.1 Slag, Skimmings and Drosses
7.1.2 Spent Linings and Refractories
7.1.3 Wastes and Residues from Pollution Abatement Systems
7.1.4 Wastes and Residues from Effluent Treatment
7.1.5 Wastes and Residues from Hydrometallurgical Processes
7.2 Management of Wastes and Residues
7.2.1 Recycling
7.2.2 Re-use
7.2.3 Disposal

This section summarizes the best practices for the reduction in the quantities of wastes generated and for the management of wastes and residues.

As each smelter has its own input and output feeds, it is difficult to make generalizations which can be applied across the whole base metals smelting sector. It must be recognized that each of these recommendations will not apply in all cases.

The recommendations establish a general direction and are, therefore, general in nature. The recommendations need to be tailored by each facility to reflect facility-specific considerations. When applied to a specific facility, these recommendations should lead to successful minimization, recycle and re-use of residues and minimization of wastes.

7.1 Minimization of Wastes and Residues

7.1.1 Slag, Skimmings and Drosses

The amount of slag, skimmings and drosses produced is dependent on the impurities in the raw materials and typically cannot be significantly reduced. In some cases, the selection of cleaner raw materials lead to reduced generation of these wastes/residues. The limited availability and higher costs of these concentrates means this is not a global solution. It should be noted that higher grade concentrates could mean that more impurities have been removed during the milling process and that increased wastes (i.e., tailings) are generated at this earlier stage of the metals production.

The generation of slags, skimmings and drosses can be minimized by optimizing furnace operations.

7.1.2 Spent Linings and Refractories

Spent linings and refractories cannot be avoided, but can be minimized by the following measures:

• Careful construction of the brick lining of the furnace;
• Continuous use of furnace to minimize variations in temperature;
• Shorten impact time of fluxing agents;
• Avoidance of aggressive fluxing agents;
• Careful cleaning of furnaces and crucibles; and
• Reduction of furnace agitation.
  

7.1.3 Wastes and Residues from Pollution Abatement Systems

Volumes of flue gas produced can often be reduced by using oxygen or oxygen enriched air for combustion instead of atmospheric air which has a greater volume per unit of oxygen. Smaller volumes of off-gas result in lower volumes of dust.

The quantity of spent filter bags may be decreased by using modern filter materials that are more robust.

7.1.4 Wastes and Residues from Effluent Treatment

The amount of wastewater that is generated by a wet scrubber can be reduced if the water is recycled back to the scrubber. A bleed stream is still required to avoid a build-up of material.

7.1.5 Wastes and Residues from Hydrometallurgical Processes

The amount of jarosite generated can be minimized by optimizing the flotation process at the mill to increase zinc recovery and the extent of iron rejection, thereby reducing the quantity of iron waste generated at the zinc plant.

Residues from zinc refining can also be reduced by switching to the goethite process. The iron residue from the goethite process is approximately 25 to 30% less by volume than the waste generated from the traditional jarosite process.

7.2 Management of Wastes and Residues

7.2.1 Recycling

Efforts should be made to recycle residues internally.

Dusts resulting from off-gas treatment systems should be recycled to smelting furnaces.

Slags should be treated to recover metals which can be recycled to the process.

7.2.2 Re-use

Re-use options should be identified for all residues which cannot be recycled on site. Not all materials will be re-usable but consideration should be given to re-use options.

Alternative uses of residues should be explored and marketed where feasible.

As identified in the Base Metals Smelting Sector Strategic Options Report, barriers to the re-use of residues should be reviewed and modified to increase the level of re-use of residues.

7.2.3 Disposal

Disposal should only be considered when there are no possibilities for recycle or re-use.

Wastes should be disposed of in an environmentally-sound manner.

Wastes should be fixed, if required, to eliminate/reduce leaching potential prior to disposal. The leaching potential should be determined using standard leaching protocols as identified in regulations.

Consideration should be given to the eventual decommissioning of on-site disposal areas.

Mary Ann Crichton
Practice Director
Hatch Consulting

MAEC:gc