Metal Recovery From Spent Mercury And H2S Absorbents
Authors: Pornsakulsak Lawan , Soponkanabhorn Teerapon 
Published: December 2007

Mercury recovery has been widely-practiced in the E&P business, particularly during mercury contaminated waste disposal of sludge, spent mercury and hydrogen sulfide absorbents. However, recovery of other metals in spent absorbents has not been widely explored or considered during the waste treatment process. For this reason, this study on the management of these wastes was conducted to ensure environmentally sound company operations, cost effectiveness and sustainable development.

Mercury and hydrogen sulfide absorbents were firstly applied in the natural gas purification process of PTT Exploration & Production Co. Ltd. at the Bongkot Production Platform to remove mercury and hydrogen sulfide absorbents in November 2005. After their use, service, spent absorbents were discharged from mercury the removal unit (MRU) and Sour Gas Recovery Unit (SRU) and transferred to storage at the company's onshore supply base before their appropriate disposal.

Information gathered from material data sheets indicated the possibility of worthwhile metal recovery from the spent absorbents. Moreover, waste sampling and laboratory analyses were also conducted to gain a full understanding of waste's characteristics. Some specific parameters were employed in waste classification. Mercury, copper, zinc and sulfide were analyzed for both Total Threshold Limit Concentration (TTLC) and Soluble Threshold Limit Concentration (STLC). Besides, potential recoverable metals e.g. copper and zinc were analyzed. Local and international legislation were also reviewed to help make any final decisions regard the most appropriate waste treatment technology.

It was recommended that high mercury spent absorbents be retorted and roasted to remove the mercury before its transfer to a recovery plant for copper or zinc recovery. It was furthermore decided that low mercury absorbent should be sent to a metal recovery plant directly without any treatment.

As a result of this study, it was found that, with proper waste management, metal recovery from spent absorbents could provide considerable financial and environmental while also reducing, especially in terms of reducing disposal cost.

Introduction

Metals play an important part in modern societies and have historically been linked with industrial development and improved living standards, Society can draw on metal resources from the Earth's crust as well as from metal discarded after use in economy. Inefficient recovery of metals increases an economy's reliance on primary resources and can impact nature by also increasing the dispersion of undesirable metals in ecosystems. The practice of recovering metals for their value dates back to ancient civilizations, but even greater protection of Earth's resource endowments and ecosystems adds to our incentive for recovering metals after use.

Since mercury and hydrogen sulfide (H2S) absorbents, which are metal-based, were selected to be absorbents used for PTTEP operations in Bongkot field, consideration for environmental sound operations of on the spent material disposal have been studied. This careful scrutiny is in line with PTTEP's Waste Management Standards (PTTEP, 2000)1 which emphasizes "options for reduction, reuse, recycling or recovery shall be considered before any wastes are designated for disposal".