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Contact Section - Catalysts - Recycling/Disposal
January 18, 2003

Introduction

Over the course of normal plant operation, the pressure drop across the catalyst beds will increase due to the accumulation of dust in the beds and the normal breakdown of the catalyst itself.   Operation and maintenance of a sulphuric acid plant requires that the catalyst in the converter be periodically removed, screened and reinstalled into the converter to return the pressure drop to normal.  The screening operation separates the dust and catalyst fines that have accumulated in the beds.  As well, the mechanical handling of the catalyst also breaks down the catalyst to a certain degree creating additional fines.  In some cases entire beds must be replaced due to deactivation of the catalyst, contamination, changes in suppliers, etc.  All these activities leads to the creation of a waste stream that must be properly handled and disposed of to prevent damage to the environment.

Recovery of vanadium from spent sulphuric acid catalyst is an integral part of most vanadium producers operations.  The vanadium content of spent catalyst is often higher than ores and is the preferred feedstock for some producers.

Vanadium is recovered from spent catalyst using one of two methods; Hydrometallurgy or Pyrometallurgy.

Hydrometallugy

The recovery of vanadium starts with the crushing and blending of the feedstock followed by chemical extraction and leaching.

Pyrometallurgy

The pyrometallurgical route involves traditional smelting and refining methods.  This route is generally not economical unless large quantities of spent catalyst is being processed and vanadium metal prices are high.

Recycling

The vanadium content in spent catalyst can be recycled as vanadium salts or as ferrovanadium for steel production.  Generally recyclers of spent sulphuric acid catalysts will require a sample of the material prior to accepting the material for recycling.  The spent catalyst cannot contain toxic elements or radioactive materials. 

In all cases of the recycling versions it is very important that the spent catalyst has a low content of arsenic. A typical analysis for spent catalyst:-

V2O5: min. 3% weight
K2O: max. 10% weight
P: max. 0.5% weight
Sn, Pb, As, Sb, Bi, Cu, Zn, Cd, Hg: max. 0.1% weight

Recyclers will generally specify the type of packaging for the spent catalyst to meet their own handling requirements.  A material safety data sheet should accompany the shipment.

Landfill Disposal

Two types of disposal are available:

Fixation

The catalyst is ‘fixed’ in an inert matrix, usually concrete or glass (also known as vitrification) prior to controlled deposit in a suitably licensed landfill site. The fixation process is  designed to prevent metals leaching into the landfill site.

Direct Landfilling

The catalyst is deposited directly into a suitably licensed landfill site in compliance with national legislation. It is common practice to mix the catalyst with lime to neutralise residual acidity.

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