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

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.Acid mine drainage (AMD) is caused by the oxidation of sulfur-bearing materials in the presence of oxygen and water, resulting in sulfate and metals solubilization and forming acidic solutions 1-4 . Active and inactive mining activities for metals, such as copper, lead, zinc, gold, silver and uranium, provoke potential degradation of the environment by the presence of different contaminants, particularly due to metals and sulfates in acid drainage 5 . Indeed, the acid drainage formation is an important environmental aspect of mining practices. The sulfate concentrations may reach 2,400 to 20,800 mg/L 6,7 , well above the limit of 250 mg/L established by the World Health Organization 8 . It might cause damage not only to human health but also to the environment, and depreciation of structures and equipment 2,9 , resulting in high costs for control and management by the mining companies 2,10 . Copper concentration may be in the range from 77 to 615 mg/L, with higher values in the Cu mines 1,11 . Other metals such as Al, Mn, Fe, Mg, and Zn are also commonly found in AMD in these mines 10,12 .AMD remediation can be actively accomplished off-site with the pumping of the contamination plume to a treatment plant, or passively on-site with the use of permeable reactive barriers (PRB), with lower installation and maintenance costs. It can be carried out with the flow directed to the system, by the Funnel model, or the grid-type, by the installation of a perpendicular barrier to the contamination plume 13,14 . The PRB was first proposed in Canada in the 1990s 13,15 , with different materials used as adsorbent media, from single barriers with only one material to composites of different materials, or multiple sequential barrier...

Removal of Cr(III) From Water By Polyurethane Foam Incorporated With Green Liquor Dregs Waste

“…Most of the wastes leftover from pulp and paper industry have an alkaline character with pH values up to 13.0 (Quina and Pinheiro, 2020). Regarding the pzc of 8.40 obtained for the dregs, the high efficiency of this residue at pH 6 is probably related to the presence of carbonates and hydroxides, which suggests a potential for adsorption of anionic ions (Farage et al, 2020). The foam surface is positively charged at pH 6, although electrostatic repulsions may occur below the pcz, yielding a reduced adsorption (Kumari et al, 2016).…”

“…The high pzc of the dregs is also due to the presence of Ca compounds. Farage et al (2020) reported a pzc of 9.75 for another dregs waste. Most of the wastes leftover from pulp and paper industry have an alkaline character with pH values up to 13.0 (Quina and Pinheiro, 2020).…”

“…The pH values were measured using a pH meter and the PZC was obtained after plotting ΔpH (pH final -pH initial) against the initial pH. This methodology was adapted from that described by Farage et al (2020).…”

Inorganic Waste Generated in Kraft Pulp Mills: The Transition from Landfill to Industrial Applications

“…Metal removal and neutralization of acid mine drainage (AMD) in treatment systems can be controlled by the addition of alkaline SG [62,63].…”

“…A mixture of SG and green liquor sludge (7 t/ha) buffered soil acidity [38]. 0.96 tons of SG would be required to replace 1 ton of a commercial ground limestone product [63].…”