Radiographic film waste management in Thailand and cleaner technology for silver leaching

摘要

In Thailand, a large amount of radiographic film waste is generated in hospitals. Fixer and developer solutions removed approximately 35 - 45% of the sensitive silver compounds from the films, depending on the object exposed. Solutions are reused twice, while used films are kept for the records for more than 5-10 years. After that, these wastes are sold to dealers. More than 90% of the dealers are not officially registered. Wastes are delivered to in-house factories to recover silver either by electrolysis, acid leaching (HNO_3) or combustion process. Most waste processors are not really concerned with handling the wastes. Highly toxic chemicals are generally spilled and discharged into the environment. The cleaner technology concept of silver leaching from radiographic film was investigated using weak acids such as acetic, oxalic and malonic acids. The tests were carried out under low temperature conditions. An oxalic acid solution at 5% (w/v) provided the best leaching condition at 100℃ for 20 min. This achieved 100% silver leaching from the films. The obtained silver was in its metal form and ready for ingot production. Following this, a fact sheet on the waste management of radio-graphic film waste was created to reduce the risks of spills and leakages of hazardous silver into the environment.