Chemical Origin of Phosphine in Nature

Phosphine (PH₃) is a natural gaseous carrier of phosphorus in its biogeochemical cycles, has been found ubiquitously present in the environment. The origin of phosphine in various environmental sites is still under debated, although phosphine evolution used to be reported from microbial habitats. The tentative experiments show that phosphine gas could be produced by aqueous or acid corrosion from phosphorus-containing impurities in iron. The concentration of phosphine liberated by aqueous corrosion was of the same order of magnitude (ng/kg) as those detected in natural environment. Acid could accelerate corrosion and promote the production of phosphine. The quantity of phosphine liberated by 0.5 mol/L sulfuric acid corrosion was three magnitude orders (ug/kg) higher than that in aqueous corrosion, which may provide a convincing explanation for the significant occurrence of phosphine in strong acidic condition (landfill gas, anaerobic fermentation gas, etc). It was shown that phosphine emission in air as headspace gas was higher than in nitrogen gas under aqueous corrosion, while different headspace gas (air or nitrogen gas) showed little effect on phosphine liberation by acid corrosion. Phosphine produced by reduced type iron powder (analytical reagent) was lower than by technical iron filings. Iron filings after grinding could enhance the emission of phosphine. Under acid corrosion, an exponential positive correlation between the weight of iron filings(x, g) and phosphine production concentration (y, ng/m³) has been established (y, = 58.49lnx + 343, R² = 0.9561, n = 18). A positive correlation between the concentrations of acid and phosphine production could also be observed. Results suggested that chemical corrosion of phosphorus-containing in iron filings could be considered as a source of phosphine emission in the environment. Further studies should examine the phosphorus species existing in iron and evaluate the chemical process responsible for the production of phosphine by iron corrosion.