Stripping agent and method of use

Abstract

A method of removing mercury adsorbed onto activated carbon is provided. The method includes treating an adsorbed mixture of metal cyanide complexes on a carbon substrate with an acidic solution of a stripping agent that is a weak acid. The method also eliminates inorganic scalants from the carbon substrate. In precious metal mining operations, the disclosed method reduces environmental emissions of mercury during the gold elution and carbon reactivation processes.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims the benefit of U.S. Provisional Application No. 61 / 345,769, filed May 18, 2010; and U.S. Provisional Application No. 61 / 417,133, filed Nov. 24, 2010, which are hereby incorporated by reference herein in their entirety.GOVERNMENT LICENSE RIGHTS[0002]This invention was made with government support under contract DE-FC26-02NT41607 awarded by the Department of Energy. The government has certain rights in the invention.TECHNICAL FIELD[0003]The present disclosure relates to stripping agents and their uses, including removing mercury and inorganic sealants from activated carbon used in mining or metal recovery operations.BACKGROUND[0004]Precious metal production has evolved over the past several decades, and is based principally on the ability to dissolve precious metals using a lixiviant, such as a basic aqueous cyanide solution, to form soluble metallocyanide complexes. Gold and silver are most notably recovered, but of...

AI Technical Summary

Benefits of technology

The patent describes a way to reduce mercury emissions in precious metal mining operations. It involves washing a mixture of mercury and gold that is adsorbed on activated carbon with a solution containing a weak acid to remove mercury from the carbon. The carbon is then regenerated by heating to volatilize any remaining mercury. This method helps to minimize the amount of mercury emitted during the mining process.

Problems solved by technology

While this technique is quite efficient and has been used widely in the mining industry for over 50 years, it is not without its problems.

The most notable problem arises from the fact that ores often contain other substances, such as metals or scalants, which can also be adsorbed with the favored precious metal metallocyanide complexes.

This “contaminant” is a problem from many standpoints.

First, the adsorbed mercury cyanide complexes occupy space on the activated carbon, thereby reducing the space available for adsorbing the favored precious metals.

Secondly, the mercury generally follows the precious metals in subsequent processes, requiring additional and expensive processing steps to remove and recover the mercury separately from the gold and silver.

Thirdly, mercury is a strictly regulated “toxic substance” that must be handled with expensive processes to minimize or eliminate its release to the environment.

However, a significant percentage of the mercury will remain affixed to the carbon after elution, reducing the effectiveness of the carbon as it is recycled to process more solution.

In fact, inorganic and / or organic fouling is a recurring problem in gold and silver production facilities.

However, any mercury that is not desorbed from the activated carbon can also become volatilized from the carbon in the high-temperature regeneration (or reactivation) process, and may be potentially emitted to the environment.

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