The recycling of lost phosphorus (P) is important in sustainable development. In line with this objective, biochar adsorption is a promising method of P recovery. Therefore, our study investigates the efficiency and selectivity of magnesium modified corn biochar (Mg/biochar) in relation to P adsorption. It also examines the available P derived from postsorption Mg/biochar. Mg/biochar is rich in magnesium nanoparticles and organic functional groups, and it can adsorb 90% of the equilibrium amount of P within 30 min. The Mg/biochar P adsorption process is mainly controlled by chemical action. The maximum P adsorption amount of Mg/biochar is 239 mg/g. The Langmuir-Freundlich model fits the P adsorption isotherm best. Thermodynamics calculation shows ∆H > 0, ∆G < 0, ∆S > 0, and it demonstrates the P adsorption process is an endothermic, spontaneous, and increasingly disordered. The optimal pH is 9. The amounts of P adsorbed by Mg/B300, Mg/B450, and Mg/B600 from swine wastewater are lower than that adsorbed from synthetic P wastewater by 6.6%, 4.8%, and 4.2%, respectively. Mg/biochar is more resistant to pH and to the influence of coexisting ions than biochar. Finally, postsorption Mg/biochar can release P persistently. The P release equilibrium concentrations are ordered as follows: Mg/B600 > Mg/B450 > Mg/B300. The postsorption Mg/B300, Mg/B450, and Mg/B600 can release 3.3%, 3.9%, and 4.4% of the total adsorbed P, respectively, per interval time.

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The effect of carbon risk on the debt capital market has become increasingly prominent under carbon constraints. We use a panel regression model to examine the relationship between carbon risk and the cost of debt financing and the moderating effect of positive media attention on this relationship. Using a sample of 191 Chinese A‐share listed firms operating in high‐carbon industries covering the period 2011–15, we conduct an empirical study and find that the relationship between carbon risk and the cost of debt financing in China is a U‐shaped one. Thus, carbon risk exerts an “interval effect" on the cost of debt financing, which mainly exists in private firms rather than state‐owned firms. This relationship can be mitigated by positive media attention. Compared with private firms that receive low positive media attention, private firms with high positive media attention are more sensitive and less tolerant to environmental regulations. Our findings provide firms with practical advice on carbon risk management, particularly on improving carbon transparency and mitigating the cost of debt financing.

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