The balance between photosynthetic organic carbon production and respiration controls atmospheric composition and climate1,2. The majority of organic carbon is respired back to carbon dioxide in the biosphere, but a small fraction escapes remineralization and is preserved over geological timescales3. By removing reduced carbon from Earth’s surface, this sequestration process promotes atmospheric oxygen accumulation2 and carbon dioxide removal1. Two major mechanisms have been proposed to explain organic carbon preservation: selective preservation of biochemically unreactive compounds4,5 and protection resulting from interactions with a mineral matrix6,7. Although both mechanisms can operate across a range of environments and timescales, their global relative importance on 1,000-year to 100,000-year timescales remains uncertain4. Here we present a global dataset of the distributions of organic carbon activation energy and corresponding radiocarbon ages in soils, sediments and dissolved organic carbon. We find that activation energy distributions broaden over time in all mineral-containing samples. This result requires increasing bond-strength diversity, consistent with the formation of organo-mineral bonds8 but inconsistent with selective preservation. Radiocarbon ages further reveal that high-energy, mineral-bound organic carbon persists for millennia relative to low-energy, unbound organic carbon. Our results provide globally coherent evidence for the proposed7 importance of mineral protection in promoting organic carbon preservation. We suggest that similar studies of bond-strength diversity in ancient sediments may reveal how and why organic carbon preservation—and thus atmospheric composition and climate—has varied over geological time.Broadening activation energy distributions and increasing radiocarbon ages reveal the global importance of mineral protection in promoting organic carbon preservation.

Mineral protection regulates long-term global preservation of natural organic carbon

Using FTIR-photoacoustic spectroscopy for phosphorus speciation analysis of biochars.

The effect of different pyrolysis temperatures on the speciation and availability in soil of P in biochar produced from the solid fraction of manure

Minerals stabilize organic carbon (OC) in sediments, thereby directly affecting global climate at multiple scales, but how they do it is far from understood. Here we show that manganese oxide (Mn oxide) in a water treatment works filter bed traps dissolved OC as coatings build up in layers around clean sand grains at 3%w/wC. Using spectroscopic and thermogravimetric methods, we identify two main OC fractions. One is thermally refractory (>550 °C) and the other is thermally more labile (<550 °C). We postulate that the thermal stability of the trapped OC is due to carboxylate groups within it bonding to Mn oxide surfaces coupled with physical entrapment within the layers. We identify a significant difference in the nature of the surface-bound OC and bulk OC . We speculate that polymerization reactions may be occurring at depth within the layers. We also propose that these processes must be considered in future studies of OC in natural systems.

Data from: Towards a mechanistic understanding of carbon stabilization in manganese oxides.

New insights into the interaction between heavy metals and struvite: Struvite as platform for heterogeneous nucleation of heavy metal hydroxide

Struvite (MgNH4PO4·6H2O) was heated to temperatures from 55 to 300 °C. X-ray diffraction analysis revealed struvite was stable at 55 °C, partially decomposed to dittmarite (MgNH4PO4·H2O) at 100–200 °C, and formed an amorphous phase at 250–300 °C. Thermogravimetric analysis confirmed sample mass loss consistent with dittmarite formation at 100–200 °C and evolution of all volatiles at 250–300 °C. Fourier transform infrared (FTIR) spectroscopy detected the ν4 NH
 4
 +
 band in 55–200 °C solids, as expected for struvite and dittmarite. This band decreased in intensity at 250 °C, and was not evident at 300 °C, confirming loss of NH
 4
 +
 (s) at these temperatures. FTIR spectra also showed changes in the vibrations of the ν3 PO
 4
 3−
 band. At 55 °C, splitting in the band indicated destabilization of the PO
 4
 3−
 (s) group despite no change in mineralogy. Vibrations at 100–200 °C were associated with dittmarite and MgHPO4, and at 250–300 °C, MgHPO4 and Mg2P2O7. Analysis of acid-digested solids indicated the presence of P other than P–PO4 at 200–250 °C, confirming Mg2P2O7 formation. Overall, heat treatment of struvite produces several decomposition products, complete identification of which requires the use of multiple approaches. Temperature-induced phase transformations along with emission of NH3(g) have implications for use of struvite in multiple applications.

An investigation of the thermal behavior of magnesium ammonium phosphate hexahydrate

Struvite (MgNH4PO4·6H2O) can be recovered from wastewaters for mitigation of phosphorus content. However, the interaction of dissolved constituents with struvite is rarely evaluated. Removal of heavy metals and total organic carbon (TOC) in a greenhouse wastewater (GW) by struvite was investigated. Presynthesized struvite was added to GW and removal of Zn (689 μg/L), Cu (151 μg/L), and TOC (51 mg/L) monitored from 1 to 26 d. Metal uptake in sodium nitrate solutions was used to assess competition, and the influence of other GW constituents on sorption. Struvite was also directly precipitated from GW (PPT). Recovered GW solids had 64–247 mg/kg Zn, 12–54 mg/kg Cu, and 1721–8806 mg/kg TOC, with lowest loadings for PPT and highest for 26 d solids. X-ray absorption spectroscopy detected polymerized Zn-phosphate, induced by dissolved phosphorus in GW, and Cu copolymerization, initially limited by aqueous Cu-organic complexation. Sorbed Cu shifts Fourier transform infrared-sensitive phosphate bands and changes th...

Synergistic Removal of Zinc and Copper in Greenhouse Waste Effluent by Struvite

An aerated fluidized bed reactor (aerated-FBR) was used for recovery of orthophosphate (PO4–P) from dairy wastewater (D-WW) and swine wastewater (S-WW) by struvite (MgNH4PO4·6H2O) precipitation. Model wastewater solutions (S-model, D-model) free of organic material were also treated. The maximum PO4–P recovery for treated livestock wastes was 94% for S-WW and 63% for D-WW. The PO4–P recovery did not improve for S-model compared to S-WW, but increased to 81% for D-model relative to D-WW, suggesting that the high organic content of D-WW may hinder the recovery process. X-ray diffraction (XRD) analysis of recovered solids revealed that treated S-WW produced mostly struvite (95–98%) while D-WW yielded a mixture of struvite (28–33%), calcite (CaCO3; 17–55%), and monohydrocalcite (CaCO3·H2O; 13–42%). The Fourier transform infrared (FTIR) spectra of the solids confirm the presence of vibrational bands associated with these minerals. Simultaneous thermal analysis (STA) indicated that all solids, except for D-WW, ...

Aerated Fluidized Bed Treatment for Phosphate Recovery from Dairy and Swine Wastewater

Calcium enhances adsorption and thermal stability of organic compounds on soil minerals

Struvite-bearing solids from swine (S) and dairy (D) wastewater, heat-treated to 150-300 °C, were evaluated as ammonia gas (NH3(g)) sorbents and compared to biochar (BC) and a metal-organic framewo...

Marlon V. Ramlogan

Papers

An investigation of the thermal behavior of magnesium ammonium phosphate hexahydrate

Synergistic Removal of Zinc and Copper in Greenhouse Waste Effluent by Struvite

Aerated Fluidized Bed Treatment for Phosphate Recovery from Dairy and Swine Wastewater

Calcium enhances adsorption and thermal stability of organic compounds on soil minerals

Thermochemical Analysis of Ammonia Gas Sorption by Struvite from Livestock Wastes and Comparison with Biochar and Metal-Organic Framework Sorbents.