Case study : the prospect of using nature-derived chemicals for removing metals from acid mine drainage in Folldal, Norway

Abstract

Folla is one of Norway’s most affected rivers by acid mine drainage today. Acidic water with a high concentration of metals is formed during pyrite oxidation in the spoil masses from Folldal Mines in Folldal centre, discharging into Folla and making it inhabitable for aquatic life. After many years of investigation of different solutions to the problem, The Directorate of Mining proposed a three-step solution in early 2022. One of the solutions proposed is the active treatment of AMD. This study investigates the use of nature-derived chemicals to remove metals from AMD. Samples were first collected for preliminary tests. Later was chitosan, a biopolymer, used in experiments with model water based on results from the preliminary tests. Chitosan was used as a primary coagulant and as an adsorbent after being modified with biochar to chitosan-covered biochar. AMD was collected a second time for adsorption batch tests with chitosan-covered biochar and jar tests with NaOH and chitosan as flocculant aid. The results show that the chitosan-covered biochar removed 99.76% of Cu, 99.83% of Al, 97.88% of Zn, and 99.99% of Fe in the acidic model water, while only removing Fe (93.54%) and Cr (53.57%) in the collected AMD. Chitosan did not remove any metal as a primary coagulant. Chitosan as a flocculant aid did not disrupt the removal of metals through conventional methods; an increase in the sludge volume was observed. Further research is needed to investigate the use of chitosan-covered biochar and chitosan as flocculant aid.