Sludge heavy metal extraction method

The invention discloses a sludge heavy metal extraction method which comprises the following steps: converting carbon dioxide into supercritical carbon dioxide; injecting a complexing agent into supercritical carbon dioxide extraction equipment added with ethanol to extract the complexing agent; sludge is subjected to precipitation, filter pressing, drying and ultrasonic-assisted crushing, then a surfactant and the sludge are added into an extraction kettle to be extracted through a complexing agent, a heavy metal complex extraction solution is obtained through ultrasonic-assisted extraction, and carbon dioxide, a pure metal complex product and the surfactant are obtained after separation is conducted through a separator. The method has the advantages of being good in environmental protection property, high in extraction efficiency, high in speed, wide in application range and easy to recycle after extraction, ultrasonic-assisted extraction improves the extraction efficiency, shortens the extraction time, red