Biochars produced from various agro-industrial by-products applied in Cr(VI) adsorption-reduction processes.

This study aimed to reuse different agro-industrial by-products (poultry litter, pig manure, sewage sludge and coffee husk) for biochar production and to evaluate their Cr(VI) removal capacities in aqueous medium. The biochars showed different morphologies with porous structures. The percentages of Cr(VI) removal from solution were higher in acid medium (pH = 2), reaching values up to 87%. For all biochars, Cr(VI) removal occurs via both adsorption and reduction, being a rapid (30 min) process, which fits best to the pseudo-second order kinetic model. The biochars, especially from coffee husk, were able to reduce up to 20% of Cr(VI) to Cr(III). The maximum Cr(VI) removal capacities ranged from 10.86 mg g-1 (sewage sludge biochar) to 18.52 mg g-1 (coffee husk biochar). Therefore, the production of biochars from the agro-industrial by-products using the same experimental conditions in one single study is important to compare the Cr(VI) removal capacities from different biomasses. Thus, this study explored the corresponding raw material without the need of further treatment. Biochars showed potential for environmental applications considering Cr(VI)-polluted environments. It is hoped to provide basis to future studies using real wastewater samples.

Combining biochar and sewage sludge for immobilization of heavy metals in mining soils.

Excess heavy metal concentrations in mining areas is a worldwide problem due to their toxicity and persistence. Applying amendments to those areas is a cost-effective remediation technique that would aid revegetation efforts. The aim of this work was to study the ability of sewage sludge-derived biochar (SSB), wood charcoal powder (hereafter named wood biochar - WB), raw sewage sludge (SS), and their blending (WB/SS) to improve soil properties and to immobilize Cd, Pb, and Zn after their addition to heavy-metal contaminated soils from a Zn-mining area. Biochar was prepared from dried sewage sludge and a greenhouse experiment was set using different amendment doses (WB = 30 and 60 g kg-1, SS = 10 and 20 g kg-1). Addition of wood biochar and sewage sludge-derived biochar to soils led to increased leachate and soil pH. Biochar materials were responsible for the greatest reduction of Cd, Pb, and Zn bioavailability. The use of sewage sludge-derived biochar or the combination of sewage sludge with wood biochar in mining areas are potential alternatives for reusing and aggregating value to these locally available wastes, offering an opportunity to solve both soil remediation and waste disposal problems at once.

Amending potential of organic and industrial by-products applied to heavy metal-rich mining soils.

Mining activities promote the development of economies and societies, yet they cause environmental impacts that must be minimized so that their benefits overcome the likely risks. This study evaluated eco-friendly technologies based on the use of low-carbon footprint wastes and industrial by-products as soil amendments for the revegetation of Zn-mining areas. Our goal was to select adequate soil amendments that can be used to recover these areas, with a focus on low-cost materials. The amendments - limestone, sewage sludge, biochar, and composted food remains - were first characterized concerning their chemical composition and structural morphologies. Soil samples (Entisol, Oxisol, Technosol) from three different areas located inside an open-pit mine were later incubated for 60 days with increasing doses of each soil amendment, followed by cultivation with Andropogon gayanus, a native species. The amendments were able to change not only soil pH, but also the phytoavailable levels of Cd, Zn, and Pb. Limestone and biochar were the amendments that caused the highest pH values, reducing the phytoavailability of the metals. All amendments improved seed germination; however, the composted food remains presented low levels of germination, which could make the amendments unfeasible for revegetation efforts. Our findings showed that biochar, which is a by-product of the mining company, is the most suitable amendment to enhance revegetation efforts in the Zn-mining areas, not only because of its efficiency and cost, but also due to its low carbon footprint, which is currently the trend for any "green remediation" proposal.

Arsenic bioaccessibility in a gold mining area: a health risk assessment for children.

High concentrations of total arsenic (As) have been measured in soils of gold mining areas of Brazil. However, bioaccessibility tests have not yet been conducted on those materials, which is essential for better health risk estimates. This study aimed at evaluating As bioaccessibility in samples from a gold mining area located in Brazil and assessing children's exposure to As-contaminated materials. Samples were collected from different materials (a control and four As-contaminated soils/sediments) found in a gold mine area located in Paracatu (MG), Brazil. Total and bioaccessible As concentrations were determined for all samples. The control soil presented the lowest As concentrations, while all other materials contained high total As concentrations (up to 2,666 mg kg(-1)) and low bioaccessible As percentage (<4.2%), indicating a low risk from exposure of resident children next to this area. The calculated dose of exposure indicated that, except for the pond tailings, in all other areas, the exposure route considering soil ingestion contributed at most to 9.7% of the maximum As allowed ingestion per day (0.3 µg kg(-1) BW day(-1)).