Changes to the IMSBC Code: Leach Residue Containing Lead

The cargo is a lead residue resulting from a metal recovery process that extracts zinc from a specifically manufactured ore or concentrate. The extraction process uses sulphuric acid and leaves an insoluble substance that is grey to brown in colour.

The residue is considered to be a sustainable and valuable secondary source of lead for further processing rather than a waste product.

The re-processed residue has a variety of uses; typically used in lead acid storage batteries, building industry, pigmentation, pipework, cable sheathing, glassware, radiation protection, solder and alloyed with other metals.

Cargo properties

Leach residue is usually extremely fine and may contain traces of lead and sulphuric acid from the extraction process.

The particles will have strong suction characteristics and retain moisture until exposed to stress from loading and/or vessel motions.

Cargo hazards

The cargo is listed in the IMSBC Code as a ‘material hazardous in bulk’ (MHB); being both corrosive and toxic. Cargoes that are listed as MHB are those that have hazards not found in the IMDG code (hazardous goods in packaged form) and are only hazardous in bulk form. Therefore, the cargo schedule is not given a UN number as per IMDG code cargoes as per section 4.1.1.3 of the IMSBC code.

The residue is also very fine, therefore posing a liquefaction hazard.

As such the cargo is listed as both GROUP A and B.

Importantly, it should be noted that there is also a hazard to humans. The cargo is corrosive to the eyes and is known to potentially cause long term health effects.

Control measures generally concern avoiding generating dust, avoiding contact or inhalation, and keeping away from naked flames and heat sources. Measure the concentration in air regularly and undertake cargo operations in the open/under local exhaust / ventilation or with respiratory protection.

The Code advises that the cargo can give off toxic gas when heated strongly (higher than 1,000°C).

The new Code schedule does not include the following hazards as identified in the original Belgian proposal to the IMO Sub-Committee on Carriage of Cargoes and Containers (ref document ‘CCC 6/INF.4’):

• H400: Very toxic to aquatic life; and
• H410: Very toxic to aquatic life with long lasting effects.

Loading and carriage of the cargo

Note that Group B cargoes should be individually listed on the vessel’s Document of Compliance (DoC) to allow carriage. Therefore, Members should check to see if their vessels’ DOCs require amending to include this new cargo.

The Master must receive a declaration in ample time prior to loading, the declaration should be fully scrutinised and not just accepted as received. The declaration should also come with a certificate of transportable moisture limit (TML) and moisture content. The tests to determine these figures must have been completed within the time frames required in the Code.

The bulk density values applied to the schedule are for a powder under laboratory conditions, therefore a bulk density of 800 to 1,600 kg/m³ may be low for a lead sulphate. As such, Members should request accurate bulk density data from the shipper.

To avoid the risk of future shortage claims, the cargo hold bilges should be pumped when required and records maintained of bilge water quantity to allow for any weight loss.

It is recommended that heat sources are kept clear of the cargo for the duration, including hot work on deck.

Crew shall wear appropriate PPE such as goggles, masks and protective overalls when potentially exposed to the cargo.

The cargo can become saturated if exposed to heavy rainfall prior to or during loading operations, therefore covered shoreside storage facilities should be provided.

At elevated moisture contents the cargo may release a potentially hazardous leachate (liquid) that requires careful handling, storage and disposal.

Shipping history

Previously cargoes are likely to have been shipped under various pre-existing IMSBC Code schedules for metal sulphide concentrates (which have similar MHB categorisations of self-heating and corrosivity as the new schedule) and mineral concentrates.

Roxburgh advise that they have seen the cargo shipped under various trade names:

• NLP (Nyrstar Leach Product): synonyms include leach residues, zinc ore, lead-contg (EC (293-314-4);
• BLP (Balen Leach Product);
• ALP (Auby Leach Product);
• BuLP (Budel Leach Product).
• Environmentally hazardous substance: lead(II)sulphate; zinc sulphate (anhydrous)).

With thanks to Roxburgh for their assistance with this article.