Acid residues remediation from mines using biochar, monopotassium phosphate and lime: Mine residues remediation with biochar, lime and phosphates

Abstract

The Zimapán mining district in the state of Hidalgo (Mexico) generates residues with high content of Cu, Pb and Zn which have been disposed for decades on sites that could cause toxicity to the surrounding area. Simultaneously, district’s water dams have been affected by an invasive plant called water hyacinth (Eichhornia crassipes), both of problems require attention and remediation treatments. The objectives of this research were: a) to evaluate biochar derived from water hyacinth (H) in mining acid residues; and b) to compare its performance vs monopotassium phosphate (F), lime (L) and the phosphates mixtures with biochar (FH) or with lime (FL) by a bioassay of barley root growth, soluble metal and pH. In this investigation four substrates was used to emulate pollution gradients: 100 %-neutral pristine soil (M1); 100 %-acid mine residues (M4); and two mixtures soil: residues (w/w) of 65:35 (M2) and 35:65 (M3). The substrates were treated with the amendment (dose w/w): H (10 %-substrate), L (3.4 %-residues), F (0.06 %-soil + 0.6 %-residues), FH (0.06 %-soil + 0.6 %-residues + 10 %-substrate) y FL (0.06 %-soil + 0.6 %-residues + 3.4 %-residues) (22 total-treatments, blanks-included). This study shows that water hyacinth could be utilized as an acid mine residues treatment by converting it to biochar. It caused the increase of root length, pH and reduce the soluble Cu and Zn as with the others amendments when the residues were present. Although the reduction of soluble Pb with biochar was considerably lower than with lime in the residues-substrates.