The present disclosure relates to magnetic composite and a process for its preparation. The magnetic composite comprise: (a) iron oxide nano-particles that are coated with at least two layers of fatty acid, (b) a biopolymer, where the second layer of the fatty acid is cross-linked with the biopolymer. The magnetic composite have a size in the range of 1.2 mm to 2.0 mm. These magnetic composite can be used for the removal of geogenic contaminants such as arsenic and fluoride compounds from the ground water source.