Phosphorus is well known as an important nutrient element associated with eutrophication in the marine ecosystem, and its sorption on sediments plays a key role in the immobilization of phosphorus in the bio-geochemical cycle. Black carbon (BC), generated from incomplete combustion of biomass and fossil fuels, becomes one part of the organic matter in sediments due to sinking into the sea via river transportation and atmospheric deposition. Although the content is low, its high micro-porosity and high specific surface make it play a significant role in sediment-water interface processes. Therefore, we prepared a black carbon from peach wood charcoal (PC) and studied its effects on phosphorus  migration  and forms distribution in sediment. The BC was derived from PC treated in HCl (2 mol L-1 ) and HCl-HF (1 mol L-1, 1 mol L-1), respectively. The sediment sample was collected from the East China Sea.

Some main conclusions are as follows, Boehm titration results showed that carboxy group of the BC was 2.149 mmol g-1, the acidic group was 2.412 mmol g-1, while the basic ones could be neglected. The BET surface area was 232.84 m2 g-1.

The sorption/desorption behaviors of phosphorus to BC were studied through batch methods. The isotherm agreed well with both Freundlich and Langmuir equation. As for the latter, Qm was 0.3427 mg g-1and Qm×KL was 0.7651 (mg g-1)(L mg-1), respectively. The hysteresis coefficient HI value is 0.667, showed an obvious sorption-desorption hysteresis.

The addition of black carbon to the sediment increased its qH-qOH, Hs, CEC and decreased pHPZNPC. The influence of BC on phosphorus sorption is significant, as the sorption capacity to BC-sediment increased from 0.0595 to 0.0891mg g-1 with the content of BC increasing from 0 to 7%. The sorption kinetic curves could be described by a two-compartment first order equation. The addition of BC reduced the rapid step fraction Frap and increased the slow step fraction Fslow, showing a significantly sorption-desorption hysteresis. The hysteresis obviously increased with an increase of black carbon contents.

The phosphorus sorbed on sediment surface was mainly consisted of Ex-P and Fe-P. After adding BC, the amounts of Ex-P and Fe-P obviously increased. Thus, the Fe and Al in the BC are favorable to the immobilization of phosphorus.