Phosphorus fractions and phosphate adsorption characteristics of 16 sediments from a shallow freshwater lake (Nansi Lake, China) and its inflow estuaries were investigated. In the present study, the sediment phosphorus is fractionated into exchangeable P (exch-P), Al-P, Fe-P, Ca-P, organic P (OP), inorganic P (IP) and total P (TP). The results show that the total phosphorus (TP) content in the sediments ranges from 571.67 to 1,113.55 mg kg(-1), and calcium bound phosphorus (Ca-P) is the main fraction of IP. The biologically available phosphorus (BAP) ranges from 32.02 to 229.67 mg kg(-1) in the Nansi Lake sediments. Phosphate adsorption on the sediments mainly occurs within 10 h and is completed within 48 h. The content of native adsorbed phosphorus (omega(NAP)) varies greatly from 6.05 to 194.37 mg kg(-1), showing a significant correlation with the total maximal amount of phosphorus adsorbed (TQ(max)). Adsorption efficiency (m) ranges from 574.79 to 3,220.68 l kg(-1) and zero equilibrium phosphorus concentration (C(EPC)) ranges from 0.010 to 0.157 mg l(-1). After the South-to-North Water Diversion Project, the inherent phosphorus present in sediments will be a major threat to the diverted water quality and be a predominant factor determining the trophic status of the lake even if the external load is reduced.

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The characteristics of phosphate adsorption and the transformation of phosphorus forms in the release process of the sediments in Nanyang Lake and Weishan Lake are researched. Distribution of maximal amount of phosphorus adsorbed (Q max) is 112.76 and 93.91 mg kg(-1), respectively, and the adsorption processes of Nanyang Lake and Weishan Lake reach equilibrium after 48 h. Total maximal amount of phosphorus adsorbed is the amount of Q max and native adsorbed phosphorus (NAP). The m is the sum of the adsorption efficiency of the sediments adsorbing the phosphorus coming from external sources and the phosphorus desorbed from the sediments. Mutual transformation between phosphorus forms exists in the process of phosphorus release. The contents of NH4Cl-P, BD-P, and HCl-P in the sediments reduced, and the content of NaOH-P increased in the process. But the amount of NaOH-P increased is less than the amount of NH4Cl-P, BD-P, and HCl-P reduced. So other forms of phosphorus transformation relations exist.

A B S T R A C TA novel method to prepare an activated red mud (activated RM) adsorbent was developed that was mainly produced from RM. The batch adsorption experiments were conducted for the study of the adsorptive performance by activated RM adsorbent. Adsorption of As(V) on activated RM was studied as a function of dosage and time. Results from the batch experiments, conducted at an initial concentration of 0.2 mg/L of As(V), suggest that arsenate removal efficiency was up to 95%. Langmuir and Freundlich isotherms equation were used to fit the adsorption isotherms. Adsorption capacity of activated RM was found to be 127.0, 111.9 and 46.7 mg/g at pH 6, 7, 9, respectively. The results indicate that there is no significant change in the equilibrium concentration after 12 h. The adsorption kinetic curve for the As(V) fit well with the pseudo-second-order equation. The leaching liquid by activated RM after the toxicity characteristic leaching procedure test can reach the Drinking water standards of China (GB 5749-2006). The adsorbent is a safe application.

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