FULL CYCLE TECHNOLOGY

The plant has three main areas:

a. Dust Treatment Area, using the rotary hearth furnace (RHF) to create zinc and iron intermediate products.

b. Zinc Oxide Area, using CML technology to create chemical grade zinc oxide and by-product lead concentrate. It also includes a sophisticated effluent treatment plant

c. Iron Melting Area, using a Submerged Arc Furnace to create pig iron and slag

a. Dust Treatment Area

The EAFD is delivered in silo trucks, in bulk sacks on trucks or in containers and discharged pneumatically into storage silos, from which it is blended prior to the addition of pulverised coal (13%). A binder is added and after intense mixing it is briquetted. Dried briquettes pass through storage bins before being screened and gently fed onto the rotating hearth of the furnace. The furnace is a circular tunnel with fixed roof and walls and a rotating floor or hearth (see film on homepage).

The RHF acts as a very high temperature (>1,250oC) circular conveyor belt. The continuous nature of the process and the re-combustion of gases in the furnace make it very energy efficient.


Simplified Full Cycle Process (indicative tonnages)

The coal in the briquettes acts as a reductant reacting with zinc and iron oxides, both of which are reduced to their metallic form. At the temperature in the furnace, zinc metal is a vapour that fumes off but quickly reacts with oxygen in the upper part of the furnace forming very fine zinc oxide particles thatb are carried away in the offgas. The iron remains in the briquette as very fine particles intimately mixed with other elements that form a slag.

In addition to zinc oxide, salt and some lead and silver compounds are also carried away in the offgas. The offgas is cooled and particulates recovered in a conventional bag filter house. This filtrate is mainly made up of zinc oxide and salt, and is referred to as Halide bearing Zinc Oxide, HZO.

After the baghouse, the offgas goes through heat exchangers before being evacuated to the atmosphere. The final offgas is compliant with local and national environmental regulations.

The furnace is heated by gas. However in order to reduce gas consumption the air injected into the RHF can be pre-heated using a biomass or other combustible material.

The treatment of EAFD in the RHF has been demonstrated at KRP and the quality of the zinc and iron intermediate products clearly demonstrated.

b. Zinc Oxide Area

The intermediate zinc oxide concentrate generated from the RHF is of exceptional quality.

These characteristics enable it to be upgraded by ZincOx’s proprietary Consecutive Metal Leaching (CML) technology, to the extent that zinc oxide alone constitutes at least 99.5% of it by weight. This level of purity is consistent with commercial grade zinc oxide chemical.

CML requires a series of washing and filtration steps under different conditions; it operates at ambient pressure and temperatures below 90OC. The plant is largely made up of agitated tanks and standard filters so there is no specialist equipment. The washing first removes chlorides and then other metals such as lead, silver and cadmium. These metals will be precipitated out principally as oxides to form a valuable lead concentrate suitable for sale to lead smelters, leaving salts as the only remaining components of the washing water. This brine will pass through a sophisticated effluent treatment plant and holding ponds so that effluent complies with limits set by environmental regulations before being discharged to the sea.

c. Iron Melting Area

The hot iron bearing briquettes which leave the RHF have a very low zinc content and consist mainly of metallic iron and slag compounds (silica, alumina, etc). They can therefore be transferred at 1,200OC directly to an electric melter where the temperature is raised to about 1,550OC, at which point melting occurs. The metallic iron sinks to the base of the furnace below the other elements which form a lighter slag layer. Both the layers are periodically tapped. The slag will be cooled in water and granulated and the iron cast as “pigs”.

Since zinc recovery in the RHF is about 95%, there will be a small amout of zinc and lead that remains in the hot briquettes. In the melter these and will be fumed off, recovered in a baghouse and sold as a zinc concentrate.

The melting furnace and associated equipment in the Iron Melting Area is of a standard design and available from numerous suppliers.