If it is bio-accumulated on the plant, the accumulation is only partial reversible or non-reversible. But if the metal is adsorbed on the plant, it should be reversible, which means you can extract. The difference between biosorption and bioaccumulation is that biosorption is a metabolically passive process, meaning it does not require energy, and the amount of contaminants a sorbent can remove is dependent on kinetic equilibrium and the composition of the sorbents cellular surface. Contaminants are adsorbed onto the cellular structure. Bioaccumulation is an active metabolic process driven by energy from a living organism and requires respiration. Bioaccumulation occurs by absorbing contaminants which are transferred onto and within the cellular surface. Both bioaccumulation and biosorption occur naturally in all living organisms.

You need to figure out how the metal is bind on the plant

before answering the question it is to clear whether you want to remove it from growing (alive) plant or from a collected sample

To Farhanullah Khan, my query is to remove the the metal after harvest.

To Xianpeng Gao

Thanks for your reply. 

salaam

that would depend on the metal. simply put the harvest should be handled in the same manor as ore specific to the given metal specified. with ore processing the first step is usually grinding to increase surface area, then chemical processes to separate unwanted material. a final step is sometimes electrolysis. depending on the % of target metal to unwanted biomass some steps might be skipped. composting, leaching, and the use of non accumulating plants should be investigated. hope that helps.

http://www.ifc.org/wps/wcm/connect/469da18048855b7f891cdb6a6515bb18/nickel_PPAH.pdf?MOD=AJPERES

http://www.udel.edu/soilchem/Chaney07JEQ.pdf

http://www.kiwiscience.com/BookChapters/Chapter15.pdf