バイオソリッドから重金属を回収する技術革新で “金字塔”(Engineers “strike gold” with innovation that recovers heavy metals from biosolids)

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2023-06-22 ロイヤルメルボルン工科大学(RMIT)

バイオソリッドから重金属を回収する技術革新で “金字塔”(Engineers “strike gold” with innovation that recovers heavy metals from biosolids)The high-value biochar produced through the patented RMIT technology. Credit: Shawn Smits Photography

◆オーストラリアのRMIT大学の研究チームは、水処理施設で発生する酸性液体廃棄物を再利用することで、重金属除去の新しい方法を開発しました。処理済み下水汚泥(バイオスラッジ)に含まれる重金属を回収し、バイオスラッジを安全に土壌改良材料として利用することが可能です。さらに、バイオスラッジを高品質のバイオチャーに変換することもできます。
◆この研究は、水処理施設や鉱山など他の廃棄物にも応用できる可能性があります。研究チームは、次に水道機関と協力して重金属除去技術の実用化を目指します。

<関連情報>

バイオソリッドから重金属を除去・回収するクローズドループの湿式冶金プロセスについて、弱酸性前処理を経由して調査した。 Investigations into the closed-loop hydrometallurgical process for heavy metals removal and recovery from biosolids via mild acid pre-treatment

Ibrahim Gbolahan Hakeem, Pobitra Halder, Shefali Aktar, Mojtaba Hedayati Marzbali, Abhishek Sharma, Aravind Surapaneni, Graeme Short, Jorge Paz-Ferreiro, Kalpit Shah
Hydrometallurgy  Available online: 2 March 2023
DOI:https://doi.org/10.1016/j.hydromet.2023.106044

Abstract

Biosolids contain heavy metals (HMs), restricting their beneficial reuse in agricultural land. However, these metals can be a valuable resource in many applications if recovered efficiently. Therefore, the removal and recovery of HMs and other limiting contaminants in biosolids without degrading the organic nutrients of the resulting treated biosolids demands holistic investigations. A closed-loop hydrometallurgical treatment process for metal removal and recovery from biosolids was developed in this study. Firstly, mild acid treatment using 3% v/v H2SO4 at 25 °C, 600 rpm for 30 min was performed in a 1 L continuous stirred tank reactor to extract common HMs (such as As, Cd, Co, Cr, Cu, Ni, Pb, and Zn) from biosolids into the aqueous phase. The effects of solids concentration and acid types on the HMs extraction efficiency were studied. Then, the primary acid leachate stream was continuously recycled for metal extraction from biosolids until the dissolved metals in the solution reached saturation concentration. After that, the dissolved metals were recovered in staged NaOH precipitation and adsorption. Low solids contents (<5% w/v) using mineral acids having pH <2 and oxidation-reduction potential (ORP) ∼500 mV (versus SHE) favoured HMs solubilisation from biosolids with an average extraction efficiency of 70%. The dissolution of ferric iron (Fe3+) by H2SO4 and subsequent in-situ formation of ferric sulfate enhanced the metal extraction strength of the spent leachate stream during recycling. However, the solids loading in each leaching process must be kept low to prevent ferric concentration build-up and precipitation as the leachate pH steadily increases above 2 during recycling. Amongst the metal recovery methods investigated, H2O2 oxidation prior to 2-stage NaOH precipitation had the highest efficiency with 75–95% HMs recovery. The clarified stream was used to neutralise the acidic treated biosolids to close the process loop. The complete process flowsheet was developed with mass balances, and the fate of nutrients (mainly C, N, and P) and major per– and polyfluoro alkyl substances (PFAS) were overviewed.

1102水質管理
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