This invention relates to a process for treating acid mine drainage (AMD). The process includes the steps of adjusting the pH of the AMD to be in the range of 3 to 5; adding maghemite nanoparticles to form a slurry; and a) aerating the slurry obtained in step 3), or b) simultaneously heating and mixing the slurry obtained in step 3). Thereafter maghemite nanoparticles loaded with one or more metals and sulphate and precipitated metals is separated from the slurry.