Transformation of Iminodi(methylene phosphonate) on Manganese Dioxides – Passivation of the Mineral Surface by (Formed) Mn2+,Environmental Science & Technology

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Transformation of Iminodi(methylene phosphonate) on Manganese Dioxides – Passivation of the Mineral Surface by (Formed) Mn2+
Environmental Science & Technology ( IF 10.8 ) Pub Date : 2023-07-29 , DOI: 10.1021/acs.est.3c01838
Anna M Röhnelt ₁ , Philipp R Martin ₁ , Daniel Buchner ₁ , Stefan B Haderlein ₁

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Aminopolyphosphonates (APPs) are strong chelating agents with growing use in industrial and household applications. In this study, we investigated the oxidation of the bisphosphonate iminodi(methylene phosphonate) (IDMP) – a major transformation product (TP) of numerous commercially used APPs and a potential precursor for aminomethylphosphonate (AMPA) – on manganese dioxide (MnO₂). Transformation batch experiments at pH 6 revealed AMPA and phosphate as main TPs, with a phosphorus mass balance of 80 to 92% throughout all experiments. Our results suggest initial cleavage of the C–P bond and formation of the stable intermediate N-formyl-AMPA. Next, C–N bond cleavage leads to the formation of AMPA, which exhibits lower reactivity than IDMP. Reaction rates together with IDMP and Mn²⁺ sorption data indicate formation of IDMP-Mn²⁺ surface bridging complexes with progressing MnO₂ reduction, leading to the passivation of the mineral surface regarding IDMP oxidation. Compound-specific stable carbon isotope analysis of IDMP in both sorbed and aqueous fractions further supported this hypothesis. Depending on the extent of Mn²⁺ surface concentration, the isotope data indicated either sorption of IDMP to the mineral surface or electron transfer from IDMP to Mn^IV to be the rate-limiting step of the overall reaction. Our study sheds further light on the complex surface processes during MnO₂ redox reactions and reveals abiotic oxidative transformation of APPs by MnO₂ as a potential process contributing to widespread elevated AMPA concentrations in the environment.

中文翻译：

亚氨基二（亚甲基膦酸酯）在二氧化锰上的转化 - 通过（形成的）Mn2+钝化矿物表面

氨基多膦酸盐 (APP) 是强螯合剂，在工业和家庭应用中的应用越来越广泛。在这项研究中，我们研究了双膦酸酯亚氨基二（亚甲基膦酸酯）（IDMP）——许多商业应用的 APP 的主要转化产物（TP）以及氨甲基膦酸酯（AMPA）的潜在前体——在二氧化锰（MnO 2 ）上的_氧化。pH 6 下的转化批次实验表明 AMPA 和磷酸盐是主要的 TP，在所有实验中磷质量平衡为 80% 至 92%。我们的结果表明 C-P 键最初断裂并形成稳定的中间体N -甲酰基-AMPA。接下来，C-N 键断裂导致 AMPA 的形成，其反应活性低于 IDMP。反应速率以及IDMP和Mn ²⁺吸附数据表明随着MnO ₂的进展，IDMP-Mn ²⁺表面桥联络合物的形成，导致矿物表面与IDMP氧化有关的钝化。对吸附馏分和水馏分中 IDMP 的化合物特异性稳定碳同位素分析进一步支持了这一假设。根据 Mn ²⁺表面浓度的程度，同位素数据表明 IDMP 吸附到矿物表面或从 IDMP 到 Mn ^IV的电子转移是整个反应的限速步骤。我们的研究进一步揭示了 MnO _{2氧化还原反应过程中复杂的表面过程，并揭示了 MnO}₂对 APP 的非生物氧化转化是导致环境中 AMPA 浓度普遍升高的潜在过程。

更新日期：2023-07-29

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