Performance of Physically and Chemically Activated Biochars in Copper Removal from Contaminated Mine Effluents

The increasing global demand for metals and minerals justifies the intensive study of treatment options for contaminated mine effluents. The present study evaluated the conversion of wood residues into physically and chemically activated biochars and their subsequent use in the treatment of Cu in synthetic and actual contaminated mine drainage. First, wood residues were converted into biochar by fast pyrolysis. Then, physical (using steam or CO2) or chemical (using KOH) activation was carried out in a homemade pilot-scale furnace. After activation, highly microporous (KOH materials) and micro/mesoporous activated biochars (CO2 and steam materials) were obtained. Batch adsorption testing was first conducted with synthetic effluents. Results showed that CO2-activated biochar was the most Cu effective adsorbent (99% removal) at low concentrations (5–20 mg L−1). The mechanisms of Cu2+ adsorption involved physical and chemisorption for biochars and CO2-activated biochar, while chemisorption for KOH-activated biochars was probably due to the high proportion of functional groups connected to their surface. In multi-metal acid mine drainage, metal adsorption capacities deteriorated for most of the materials, probably due to the effects of ion competition. However, KOH-activated biochar decreased Cu2+ concentrations to below the authorized monthly mean allowed by Canadian law (0.3 mg L−1) and decreased Co, Pb, and Mn concentrations up to 95%. These findings indicate that high porosity and oxygenated functional groups connected to the surface of activated biochars are important properties for the enhancement of interactions between carbon materials and metals from mine effluents, as well as for their performance improvement in mine drainage treatment

Activated Biochar as an Effective Sorbent for Organic and Inorganic Contaminants in Water

Adsorption is acknowledged as effective for the removal of pollutants from drinking water and wastewater. Biochar, as a widely available material, holds promises for pollutant adsorption. So far, biochar has been found to be effective for multiple purposes, including carbon sequestration, nutrient storage, and water-holding capacity. However, its limited porosity restricts its use in water treatment. Activation of biochars, when performed at a high temperature (i.e., 900 °C) and in the presence of certain chemicals (H3PO4, KOH) and/or gases (CO2, steam), improves the development of porosity through the selective gasification of carbon atoms. Physicochemical activation process is appropriate for the production of highly porous materials. As well, the morphological and chemical structure of feedstock together with pyro-gasification operating conditions for the biochar production can greatly impact the porosity of the final materials. The effectiveness of activated biochar as adsorbent depends on porosity and on some functional groups connected to its structure, both of these are developed during activation. This study provides a comprehensive synthesis of the effect of several activated biochars when applied to the treatment of organic and inorganic contaminants in water. Results show that high aromaticity and porosity are essential for the sorption of organic contaminants, while the presence of oxygen-containing functional groups and optimum pH are crucial for the sorption of inorganic contaminants, especially metals. Finally, although activated biochar is a promising option for the treatment of contaminants in water, further research is required to evaluate its performance with real effluents containing contaminants of emerging concern

Production, characterization and application of activated biochar from wood residues

Biochar is a carbon-rich material characterized by physicochemical properties desirable in multi-disciplinary areas of science and engineering such as waste management, soil amendment, carbon sequestration, bioenergy, and degraded sites rehabilitation. However, the porosity and surface area of such materials are often very low. For example, the surface area of white birch biochar obtained by fast pyrolysis at 450°C, does not exceed 5 m2 g-1. Recently, there is growing interest of the research and industrial communities in converting biochar into activated biochar due to: i) its low-cost availability; ii) potential economic feasibility in large-scale production; and iii) its effectiveness in several applications such as the treatment (sorption) of drinking water and wastewater, energy storage, as electrodes in batteries and supercapacitors, and as catalyst support. Please click on the file below for full content of the abstract

Removal of nickel from neutral mine drainage using peat-calcite, compost, and wood ash in column reactors

ABSTRACT: The effectiveness of compost, peat-calcite, and wood ash to remove Ni from a circum-neutral-contaminated mine water was tested in continuous flow experiments. Materials were compared in 4.8-L columns at hydraulic residence times (HRT) of ∼ 16.5 h over the course of 2.5–4 months. During this period, all columns successfully treated over 400 L of synthetic contaminated neutral drainage (4.05 mg/L Ni), mainly through sorption processes. Mid-column results (HRT ∼ 9 h) indicated that wood ash was the most effective material for Ni removal, and chemical extractions revealed that retained Ni was less mobile in this spent material. The pH-increasing properties of wood ash played a major role in this material’s performance, but a pH correction would be required in the initial stages of full-scale treatment to maintain the effluent within regulatory limits (6–9.5). Scaled to full-sized, mid-column results indicated that treatment cell sizes, designed for the 1-year treatment of a high discharge (10 m3/h)–contaminated effluent (4.05 mg/L Ni), would be the smallest with wood ash (< 500 m3), followed by compost (600 ± 140 m3) and peat-calcite (720 ± 50 m3)

Production, characterization, and potential of activated biochar as adsorbent for phenolic compounds from leachates in a lumber industry site

There is growing interest in low-cost, efficient materials for the removal of organic contaminants in municipal and industrial effluents. In this study, the efficiency of biochar and activated biochar, as promising adsorbents for phenol removal, was investigated at high (up to 1500 mg L−1) and low concentrations (0.54 mg L−1) in synthetic and real effluents (from wood-residue deposits in Québec), respectively. The performance of both materials was then evaluated in batch adsorption experiments, which were conducted using a low solid/liquid ratio (0.1 g:100 mL) at different phenol concentrations (C0 = 5–1500 mg L−1), and at 20 °C. Activated biochars presented higher phenol adsorption capacity compared to biochars due to their improved textural properties, higher micropore volume, and proportion of oxygenated carbonyl groups connected to their surface. The sorption equilibrium was reached within less than 4 h for all of materials, while the Langmuir model best described their sorption process. The maximum sorption capacity of activated biochars for phenol was found to be twofold relative to biochars (303 vs. 159 mg g−1). Results also showed that activated biochars were more effective than biochars in removing low phenol concentrations in real effluents. In addition, 95% of phenol removal was attained within 96 h (although 85% was removed after 4 h), thus reaching below the maximum authorized concentration allowed by Québec’s discharge criteria (0.05 mg L−1). These results show that activated biochars made from wood residues are promising potential adsorbent materials for the efficient treatment of phenol in synthetic and real effluents

Evaluation of Arsenic Leaching Potential in Gold Mine Tailings Amended with Peat and Mine Drainage Treatment Sludge

Peat and mine drainage treatment sludge can be valorized as amendments on mine sites to stabilize gold mine tailings and reduce the potential leaching of contaminants in pore water. However, the influence of organic amendments on the mobility of metalloids and/or metals in the tailings must be validated, as the leached contaminants may vary according to their type, nature, and origin. The objective of the present study was to evaluate over time the effect of peat- and/or Fe-rich sludge amendments on the mobility of As and metallic cations in the drainage water of tailings potentially producing contaminated neutral drainage. Ten duplicated weathering cell experiments containing tailings alone or amended with peat and/or Fe-rich sludge (5-10% dry weight) were performed and monitored for 112 d. The results showed that as low as 5% peat amendment would promote As mobility in tailings' pore water, with As concentrations exceeding Quebec discharge criteria (>0.2 mg L). In addition, As(III), the most mobile and toxic form, was predominant with 10% peat, whereas organic species were negligible in all cells. The use of peat alone as organic amendment for the stabilization of tailing contaminants could increase the risk of generating As-rich contaminated neutral drainage. Conversely, the mix of only 5% Fe-rich sludge with or without peat decreased As concentrations in leachates by 65 to 80%. Further studies on the use of "peat" or "peat + Fe-rich sludge" as cover or amendment should be conducted with a focus on Fe/As and Ca/As ratios

Comparison of organic materials for the passive treatment of synthetic neutral mine drainage contaminated by nickel: Short- and medium-term batch experiments

ABSTRACT: This paper addresses the comparison of various low-cost organic materials for the passive treatment of circum-neutral pH contaminated mine water. First, the effectiveness of five organic materials to remove Ni from a contaminated neutral drainage (CND) was compared in short-term batch experiments (24 h) at various pH values. Second, based on results of the short-term experiments, two substrates (brown algae and sawdust) were eliminated and three (horticultural peat, compost, wood ash) were compared along with a new substrate (field-collected surface peat) in medium-term (56 days) batch experiments to treat CND. In these experiments, calcite was added to peat samples and all substrates performed equally well, sequestering over 97% of the Ni. Chemical extractions revealed that Ni was more strongly bound to the horticultural peat-calcite (HD-peat-calcite) residue than to the field-collected peat-calcite (LT-peat-calcite) residue. Compost, because of its higher density, was identified as the most promising candidate for sorption-based fixed-bed column experiments. Nevertheless, wood ash should not be discarded as its alkaline properties favor nickel removal

Comparison of organic materials for the passive treatment of synthetic neutral mine drainage contaminated by nickel: Adsorption and desorption kinetics and isotherms

ABSTRACT: Sorption is an effective process for the remediation of mine water with low metal concentrations. To identify promising low-cost organic sorbents for nickel (Ni), adsorption and retention properties of peat, compost, brown algae, sawdust, and wood ash were compared. Batch adsorption and desorption experiments were conducted at pH 7 in 0.05 M NaNO3 solutions to simulate the ionic strength and pH of a contaminated neutral drainage. Results of adsorption kinetic experiments were best represented by the Elovich model and the fastest rates were obtained with peat (796,075 mg g−1 min−1) and compost (791 mg g−1 min−1). Results of equilibration adsorption experiments were fitted to Langmuir and Freundlich isotherms and the highest adsorption capacities were observed for peat (around 22 mg g−1) and compost (around 9 mg g−1). Desorption experiments revealed that peat and compost adsorbed more Ni and also released a lower percentage of the adsorbed metal upon exposure to Ni-free solutions

Influence of Pyro-Gasification and Activation Conditions on the Porosity of Activated Biochars: A Literature Review

Biochar is a carbon-rich organic material that has advantageous physicochemical properties for applications in multidisciplinary areas of science and engineering, including soil amendment, carbon sequestration, bioenergy production, and site rehabilitation. However, the typically low porosity and surface area of biochars (from 0.1 to 500 m2 g−1) limits the suitability for other applications, such as catalysis, electrochemistry, energy storage, and contaminant sorption in drinking water and wastewater. Given the high global demand for activated carbon products, scientists and industrialists are exploring the potential of biochar-derived biomass as precursors for activated carbons. This review presents and discusses the available studies on activated biochars produced from various precursor feedstocks and under different operating conditions in a two-step procedure: pyro-gasification (torrefaction, slow to flash pyrolysis, and gasification) followed by activation (physical, chemical or physicochemical). Findings from several case studies demonstrate that lignocellulosic residues provide attractive precursors, and that chemical activation of the derived biochars at high temperature and long residence time produces highly porous end materials. Indeed, the porosity of activated biochars varies greatly (from 200 to 2500 m2 g−1), depending on the pyro-gasification operating conditions and the feedstock (different feedstocks have distinct morphological and chemical structures). The results also indicate that the development of highly porous activated biochars for diverse purposes (e.g., electrodes for electrochemical energy storage devices, catalyst supports and adsorbents for water treatment) would benefit both the bioeconomy and the environment. Notably, it would leverage the potential of added-value biomass as an economical, non-fossil, readily available, and renewable energy source

The influence of pilot-scale pyro-gasification and activation conditions on porosity development in activated biochars

Few studies have examined the influence of pyro-gasification and activation conditions on porosity development in activated biochars. In this context, this study investigates the effects of pyro-gasification temperature (315, 399, and 454 °C), activation temperature (700, 800, and 900 °C), and activating agent (CO2 flow rate: 2, 3, and 5 L min−1) on porosity in materials made from wood residues (black spruce and white birch). Activated biochars were prepared in a two-step process: torrefaction/fast pyrolysis in a pilot-scale plant and activation using an in-house pilot-scale furnace. Results show that the physical properties of activated biochars improved over biochars and wood residues, with fivefold greater surface area for activated birch biochar over biochars, and threefold greater surface area for activated spruce biochars. Statistical analysis results reveal that pyro-gasification and activation temperature, CO2 gas flow rate, and wood residue type significantly affected the porosity of activated biochars (at p &lt; 0.05). The main findings are as follows: i) Torrefaction or pyrolysis pre-treatment step had less impact on the porosity of activated biochars, so lower energy expenditure is required to improve product quality, i.e., porosity; ii) Activation temperature was the major variable to optimize specific surface area; by increasing from 700 to 900 °C, the average surface area for activated biochars made from both wood residues increased to nearly 120 m2 g−1; iii) pilot-scale technologies produced porous activated biochars comparable to laboratory-scale technologies which could boost incentives to use thermochemical biomass conversion, and increase the profitability with these diversified by-products in biorefinery industry