LONDON (Reuters) -The U.S. Defense Logistics Agency is planning to buy more than five million pounds of bismuth metal over the next five years to secure supplies of the material last held in the national stockpile nearly three decades ago.

Bismuth metal has numerous applications in metallurgy and defense, according to the agency, including in some ammunition, due to its ability to mimic lead.

The world's largest bismuth producer is China, accounting for 13,000 metric tons of supplies last year or more than 80% of the global total, according to U.S. Geological Survey.

China has increasingly used export restrictions to tighten control over exports of critical minerals including rare earths, gallium and germanium - materials essential for defence and military equipment.

Its restrictions typically take the form of licensing requirements, quotas and outright bans on certain exports, often citing national security or environmental concerns.

The DLA previously held bismuth in the National Defense Stockpile, but the last reserves were sold in 1997.

In its statement of work published last month, the DLA said it intends to purchase bismuth metal to "reduce the risk of availability in the bismuth metal supply chain" for Department of Defense applications.

The planned procurement totals 5.16 million pounds of 99.99% pure bismuth, with annual volumes declining from 1.23 million pounds in the first year to 854,000 pounds in the fifth year.

All production, sampling and testing must take place within the continental U.S. Contractors are required to submit detailed sampling and testing plans.

Deliveries will be made to the DLA's storage depot in Hawthorne, Nevada.