Kraft pulp mill dregs and grits as permeable reactive barrier for removal of copper and sulfate in acid mine drainage

Rogério M. P. Farage,Margarida J. Quina,Caio M. M. E. Torres,Cláudio M. Silva,Licínio Gando-Ferreira,José João L. L. de Souza

doi:10.1038/s41598-020-60780-2

Rogério M. P. Farage, Margarida J. Quina + Show 4 more

Open Access

https://doi.org/10.1038/s41598-020-60780-2

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Abstract

Mining is an essential human activity, but results in several environmental impacts, notably the contamination of ground and surface water through the presence of toxic substances such as metals and sulfates in mine drainage. Permeable reactive barriers (PRB) have been applied to remediate this environmental impact, but the high costs associated with the maintenance of this system are still a challenge. The main objective of this study was to evaluate the use of kraft pulp mill alkaline residues, known as dregs and grits, as material for PRB, and to determine their capacity for retaining copper and sulfate. The work was carried out in laboratory adsorption kinetics assays, batch assays and column tests. Tests for elemental characterization, point of zero charge, acid neutralization capacity, total porosity, bulk density and moisture of the dregs and grits were conducted. The results showed high retention of Cu due to a chemical precipitation mechanism, notably for dregs (99%) at 5 min in adsorption kinetics. The grits presented similar results after 180 min for the same assay. Sulfate retention was effective at pH below 5, with an efficiency of 79% and 89% for dregs and grits, respectively. Dregs presented the best results for acid drainage remediation, notably with a solid:liquid (S:L) ratio of 1:10.

Highlights

Mining is an essential human activity, but results in several environmental impacts, notably the contamination of ground and surface water through the presence of toxic substances such as metals and sulfates in mine drainage
High-efficiency methods for the removal of sulfates and metals in acid mine drainage (AMD) have been proposed using individual or sequential Permeable reactive barriers (PRB) filled with limestone and BaCO3, respectively, resulting in complete removal of metals and more than 70% of the sulfate, by precipitation and adsorption mechanisms[10]
Dregs and grits originating in the recovery of the chemical liquor from kraft pulp mills have usually been sent to industrial landfills

Summary

Introduction

Mining is an essential human activity, but results in several environmental impacts, notably the contamination of ground and surface water through the presence of toxic substances such as metals and sulfates in mine drainage. PRBs can be applied for the neutralization of pH and remediation of organic contaminants, especially by mechanisms of adsorption, precipitation, and biological degradation They have as their main advantage the potential for on-site treatment, and as a disadvantage the lifespan of the adsorbent materials and the maintenance costs[13]. Grits are formed mainly by CaCO3 and CaO which did not react in the slaker[26,27,28,29] Those characteristics potentiate the mechanisms of chemical precipitation and adsorption, suggesting an attractive application in the retention of metallic and sulfate ions[9,30,31,32]. Their applications in soil did not cause leachates with characteristics above the limits established by the Council of the European Economic Community in their Directive 86/278/EEC, and the values found were similar to the application of commercial limestone[25]

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