Coprecipitation of Co2+, Ni2+ and Zn2+ with Mn(III/IV) Oxides Formed in Metal-Rich Mine Waters

Abstract

Manganese oxides are widespread in soils and natural waters, and their capacity to adsorb different trace metals such as Co, Ni, or Zn is well known. In this study, we aimed to compare the extent of trace metal coprecipitation in different Mn oxides formed during Mn(II) oxidation in highly concentrated, metal-rich mine waters. For this purpose, mine water samples collected from the deepest part of several acidic pit lakes in Spain (pH 2.7–4.2), with very high concentration of manganese (358–892 mg/L Mn) and trace metals (e.g., 795–10,394 µg/L Ni, 678–11,081 µg/L Co, 259–624 mg/L Zn), were neutralized to pH 8.0 in the laboratory and later used for Mn(II) oxidation experiments. These waters were subsequently allowed to oxidize at room temperature and pH = 8.5–9.0 over several weeks until Mn(II) was totally oxidized and a dense layer of manganese precipitates had been formed. These solids were characterized by different techniques for investigating the mineral phases formed and the amount of coprecipitated trace metals. All Mn oxides were fine-grained and poorly crystalline. Evidence from X-Ray Diffraction (XRD) and Scanning Electron Microscopy coupled to Energy Dispersive X-Ray Spectroscopy (SEM–EDX) suggests the formation of different manganese oxides with varying oxidation state ranging from Mn(III) (e.g., manganite) and Mn(III/IV) (e.g., birnessite, todorokite) to Mn(IV) (e.g., asbolane). Whole-precipitate analyses by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES), and/or Atomic Absorption Spectrometry (AAS), provided important concentrations of trace metals in birnessite (e.g., up to 1424 ppm Co, 814 ppm Ni, and 2713 ppm Zn), while Co and Ni concentrations at weight percent units were detected in asbolane by SEM-EDX. This trace metal retention capacity is lower than that observed in natural Mn oxides (e.g., birnessite) formed in the water column in a circum-neutral pit lake (pH 7.0–8.0), or in desautelsite obtained in previous neutralization experiments (pH 9.0–10.0). However, given the very high amount of Mn sorbent material formed in the solutions (2.8–4.6 g/L Mn oxide), the formation of these Mn(III/IV) oxides invariably led to the virtually total removal of Co, Ni, and Zn from the aqueous phase. We evaluate these data in the context of mine water pollution treatment and recovery of critical metals.

Physicochemical Characteristics of the Birnessite and Todorokite Synthesized Using Various Methods

“…Manganese oxides can be observed in different natural forms, including manganese nodules, layers in sediments [1][2][3], hydrothermal alteration products [4], or rock varnish forms [5,6]. These minerals have also been observed abundantly in engineered systems and polluted environments worldwide, including the acid-mine-drainage (AMD)-polluted streams [7][8][9]. Majority of the manganese oxide minerals are brown-black and typically occur as intimately intermixed, fine-grained, poorly crystalline masses or coatings [10].…”

“…Birnessite is a good ion exchanger and can play an important role in controlling heavy metals and other trace metals in soil and groundwater [10,28]. Several heavy metals and toxic trace elements from the AMD-affected streams and soils can be observed in birnessite and todorokite [9]. In addition, ion-trapping properties of birnessite make it a potential negative electrode material for rechargeable lithium batteries [29][30][31]; further, it can be used as a heterogeneous catalyst [32][33][34].…”

Mineral Materials Coated with and Consisting of MnOx—Characteristics and Application of Filter Media for Groundwater Treatment: A Review

“…Other authors have identified small and dense crystalline structures in the coatings, mixed with less dense, poorly crystalline or amorphous manganese oxyhydroxides [195]. In coatings of filter media from operating groundwater treatment plants birnessite type MnO x was detected [176,183], while poorly crystalline nature is typical of this MnO x variety [112]. Jones et al [195] also reported the presence of birnessite and manganite in coatings formed on filter media.…”

“…Various forms of manganese oxide are characterized by different effectiveness of contaminant removal [2], nanowires have almost five times greater maximal adsorption capacity of strontium and caesium than nanostructured microspheres [111]. The adsorption capacity of cobalt, nickel and zinc ions varies significantly among the different MnO x with asbolane having the highest metal-removing potential, followed by birnessite and todorokite, and with manganite showing the lowest adsorption properties [112]. Feng et al [113] have investigated the synthesized manganese oxides and proved that birenssite characterized by the largest surface variable negative charge has bigger adsorption capacity on heavy metals (lead, copper, cobalt, cadmium, and zinc) than cryptomelane, todorokite, or hausmannite.…”

Understanding the role of manganese oxides in retaining harmful metals: Insights into oxidation and adsorption mechanisms at microstructure level

“…Despite these structural differences, they share similar optical properties [ 23 , 109 ]. Asbolane, a Mn(IV) hydroxide exhibiting a higher oxidation state, lacks a constant molecular formula [ 110 ]. Lithiophorite has been categorized as the third type of Mn oxide, alongside layered and tunnel structures, due to its mixed layer structure [ 111 ].…”