Fig. 5. (a) Effect of HNS on P rele

Fig. 5.
(a) Effect of HNS on P release from biochar. The equilibrium pH was about 9.0 (O-P, orthophosphate; Py-P, pyrophosphate; T-P, Total phosphorus). Error bars represent ± SE (n = 2); and (b) the ionic products of some ions which may form precipitates in the modified HNS.
Figure options
The primary reason for the decrease in P release should be that the increased amount of cations in the modified HNS reacted with orthophosphate and pyrophosphate to form various calcium and magnesium phosphates, which become precipitates on the biochar surface and are difficult to release again. Under the experimental conditions (pH around 9.0), the main species of orthophosphate (View the MathML source) and pyrophosphate (View the MathML source) may react with Ca2+ (Fig. 5b). When biochar was added to the modified HNS, Besides Ca2+, View the MathML source can also lead to the precipitation of View the MathML source when it coupled with Mg2+ (Stratful et al., 2001). The precipitation reaction between the cations and P are shown in Eqs. (S1)–(S4) in SM.

Another reason might be that the HNS enhanced the effect of “cation bridge” and supplied more active sites for re-adsorption of dissolved phosphate, which may also contribute to the decrease in the P release.

3.6. Formation, distribution, and release of orthophosphate and pyrophosphate
Crop residues are rich in K, Ca, Mg, and P. In pyrolysis process (673–873 K), the phosphorus oxides are condensed to primarily form phosphorus (V)-oxide (P4O10), and that in the presence of water, P4O10 is transformed to H3PO4 (Beck and Unterberger, 2006). Then, a fraction of H3PO4 was condensed to form H4P2O7 and reacted with metallic particles (K, Ca, Mg) to form pyrophosphates (e.g., K4P2O7, Mg2P2O7 and Ca2P2O7). The other part of H3PO4 reacted directly with the metallic particles to form a mixture of phosphate (e.g., K3PO4, Mg3(PO4)2 and Ca3(PO4)2) in small particles (

ผลลัพธ์ (อังกฤษ) 1:

fig. Five.
(A) effect of hns on p release from biochar. the equilibrium ph was about 9.0 (op, orthophosphate; py-p, pyrophosphate; tp, total phosphorus). error bars represent ± se (n = 2); and (b) the ionic products of some ions which may form precipitates in the modified hns.
figure options
.the primary reason for the decrease in p release should be that the increased amount of cations in the modified hns reacted with orthophosphate and pyrophosphate to form various calcium and magnesium phosphates, which become precipitates on the biochar surface and are difficult to release again. under the experimental conditions (ph around 9.0),.the main species of orthophosphate (view the mathml source) and pyrophosphate (view the mathml source) may react with ca2 (fig. 5b). when biochar was added to the modified hns, besides ca2, view the mathml source can also lead to the precipitation of view the mathml source when it coupled with mg2 (stratful et al., 2001). the precipitation reaction between the cations and p are shown in eqs.(S1) - (s4) in sm.

Another reason might be that the hns enhanced the effect of "cation bridge" and supplied more active sites for re-adsorption of dissolved phosphate, which may also contribute to the decrease in the p. release.

3.6. formation, distribution, and release of orthophosphate and pyrophosphate
crop residues are rich in k, ca, mg, and p. in pyrolysis process (673-873 k),.the phosphorus oxides are condensed to primarily form phosphorus (v)-oxide (p4o10), and that in the presence of water, p4o10 is transformed to h3po4 (beck and unterberger, 2006). then, a fraction of h3po4 was condensed to form h4p2o7 and reacted with metallic particles (k, ca, mg) to form pyrophosphates (eg, k4p2o7, mg2p2o7 and ca2p2o7).the other part of h3po4 reacted directly with the metallic particles to form a mixture of phosphate (eg, k3po4, mg3 (po4) 2 and ca3 (po4) 2) in small particles (<1 μm) and deposited on larger particles of biochar (. 0.01-1.0 mm) (zhang and ninomiya, 2007 and brown et al., 2009). because of the complexity of the reaction between h3po4 and metallic particles, hydrophosphate (eg, k2hpo4,.mghpo4 and cahpo4) and dihydric phosphate (eg, kh2po4 and mg (h2po4) 2) of the metals were also present in this process, which were dehydrated to form pyrophosphates finally.

in the fast pyrolysis system, the temperature at outer layer of. biochar was higher than that of inner layer. with an increase in retention time of biochar,.the small p-containing particles deposited on the surface of larger biochar particles were dehydrated to form pyrophosphates, and there were more pyrophosphates than orthophosphate in the outer layer (fig. 6). this can be used to partially explain the faster release rate of pyrophosphate in the initial 8 h, compared to that of orthophosphate. when biochar was added into water,.the ca2 and mg2 were adsorbed onto the negatively charged functional groups to form a "cation bridge" and provide the adsorption sites for anions. hence, an increase in ca2 and mg2 would re-adsorb more phosphate. the occupation of active sites in cation bridge as well as on the surface of biochar by coexisting anions reduced the re-adsorption of released phosphate,.and enhanced the p release. the release of p from biochar was influenced by many factors, besides those abovementioned.

full-size image (32 k)
fig. 6th.
Distribution of p species on biochar surface. (A) formation of orthophosphate and pyrophosphate; (b) increased pyrophosphate in the outer layer of biochar surface; and (c) release of orthophosphate and pyrophosphate from biochar in water.
.figure options
4. conclusion
in summary, the p release from biochar to water was influenced by various factors, such as retention time, coexistence anions, and other nutrient elements. the interaction between p species and the surface of bichar are based on "ion bridge", thus the cations and anions in solution could influence the migration of p.the massive produced biochars derived from different crop residues and other waste biomass would be a potential p resource to mitigate the p crisis if the p leakage was avoided by optimization of p release parameters.

acknowledgements
the authors gratefully acknowledge financial support from national 863. program (2012aa063608-01),.national key technology r & d program of the ministry of science and technology (2012baj08b00) and the key special program on the s & t for the pollution control and treatment of water bodies (no. 2012zx07103-001).

appendix a. supplementary material

ผลลัพธ์ (อังกฤษ) 2:

Fig. 5.
(a) Effect of HNS on P release from biochar. The equilibrium pH was about 9.0 (O-P, orthophosphate; Py-P, pyrophosphate; T-P, Total phosphorus). Error bars represent ± SE (n = 2); and (b) the ionic products of some ions which may form precipitates in the modified HNS.
Figure options
The primary reason for the decrease in P release should be that the increased amount of cations in the modified HNS reacted with orthophosphate and pyrophosphate to form various calcium and magnesium phosphates, which become precipitates on the biochar surface and are difficult to release again. Under the experimental conditions (pH around 9.0), the main species of orthophosphate (View the MathML source) and pyrophosphate (View the MathML source) may react with Ca2 (Fig. 5b). When biochar was added to the modified HNS, Besides Ca2 , View the MathML source can also lead to the precipitation of View the MathML source when it coupled with Mg2 (Stratful et al., 2001). The precipitation reaction between the cations and P are shown in Eqs. (S1)–(S4) in SM.

Another reason might be that the HNS enhanced the effect of "cation bridge" and supplied more active sites for re-adsorption of dissolved phosphate, which may also contribute to the decrease in the P release.

3.6. Formation, distribution, and release of orthophosphate and pyrophosphate
Crop residues are rich in K, Ca, Mg, and P. In pyrolysis process (673–873 K), the phosphorus oxides are condensed to primarily form phosphorus (V)-oxide (P4O10), and that in the presence of water, P4O10 is transformed to H3PO4 (Beck and Unterberger, 2006). Then, a fraction of H3PO4 was condensed to form H4P2O7 and reacted with metallic particles (K, Ca, Mg) to form pyrophosphates (e.g., K4P2O7, Mg2P2O7 and Ca2P2O7). The other part of H3PO4 reacted directly with the metallic particles to form a mixture of phosphate (e.g., K3PO4, Mg3(PO4)2 and Ca3(PO4)2) in small particles (<1 μm) and deposited on larger particles of biochar (0.01–1.0 mm) (Zhang and Ninomiya, 2007 and Brown et al., 2009). Because of the complexity of the reaction between H3PO4 and metallic particles, hydrophosphate (e.g., K2HPO4, MgHPO4 and CaHPO4) and dihydric phosphate (e.g., KH2PO4 and Mg(H2PO4)2) of the metals were also present in this process, which were dehydrated to form pyrophosphates finally.

In the fast pyrolysis system, the temperature at outer layer of biochar was higher than that of inner layer. With an increase in retention time of biochar, the small P-containing particles deposited on the surface of larger biochar particles were dehydrated to form pyrophosphates, and there were more pyrophosphates than orthophosphate in the outer layer (Fig. 6). This can be used to partially explain the faster release rate of pyrophosphate in the initial 8 h, compared to that of orthophosphate. When biochar was added into water, the Ca2 and Mg2 were adsorbed onto the negatively charged functional groups to form a "cation bridge" and provide the adsorption sites for anions. Hence, an increase in Ca2 and Mg2 would re-adsorb more phosphate. The occupation of active sites in cation bridge as well as on the surface of biochar by coexisting anions reduced the re-adsorption of released phosphate, and enhanced the P release. The release of P from biochar was influenced by many factors, besides those abovementioned.

Full-size image (32 K)
Fig. 6.
Distribution of P species on biochar surface. (a) Formation of orthophosphate and pyrophosphate; (b) Increased pyrophosphate in the outer layer of biochar surface; and (c) Release of orthophosphate and pyrophosphate from biochar in water.
Figure options
4. Conclusion
In summary, the P release from biochar to water was influenced by various factors, such as retention time, coexistence anions, and other nutrient elements. The interaction between P species and the surface of bichar are based on "ion bridge", thus the cations and anions in solution could influence the migration of P. The environmental conditions can be adjusted to obtain the optimum P release parameters, for instance, to adjust the amount or speed of P release by change the concentration of other nutrient elements or the anions in the soil. The massive produced biochars derived from different crop residues and other waste biomass would be a potential P resource to mitigate the P crisis if the P leakage was avoided by optimization of P release parameters.

Acknowledgements
The authors gratefully acknowledge financial support from National 863 Program (2012AA063608-01), National Key Technology R&D Program of the Ministry of Science and Technology (2012BAJ08B00) and the Key Special Program on the S&T for the Pollution Control and Treatment of Water Bodies (No. 2012ZX07103-001).

Appendix A. Supplementary material

ผลลัพธ์ (อังกฤษ) 3:

Fig. 5.
(a) of Effect HNS P on release from biochar.The equilibrium pH was about 9.0 (O - P, orthophosphate; Py - P, pyrophosphate; T - P, Total phosphorus). Error bars represent±SE (N= 2); and (b) the products of some Ionic ions which may form precipitates in the modified HNS.

Figure optionsPrimary reason for the decrease in The P release should be that the increased amount of cations in the modified HNS reacted with orthophosphate and pyrophosphate to form various calcium and magnesium phosphates, which become precipitates on the surface and are difficult to release biochar again. Under the experimental conditions (pH around 9.0,The main species of orthophosphate (View MathML the source) and pyrophosphate (View MathML the source) may react with Ca 2 (Fig. 5B) .When biochar was added to the modified HNS, Besides Ca 2, the View MathML source can also lead to the precipitation of the View MathML source when it coupled with Mg 2 (Stratful et al ., 2001). The precipitation reaction between the cations and P Eqs are shown in.(S1) - (S 4) in SM.

Another HNS enhanced the reason might be that the effect of cation Bridge" and "supplied more active sites for re-adsorption of dissolved phosphate, which may also contribute to the decrease in the P release.

3.6.Formation, distribution, and release of orthophosphate and pyrophosphate
Crop residues are rich in K, Ca, Mg, and P.In pyrolysis process (673 - 873 K),The phosphorus oxides are condensed to form primarily phosphorus (V) -oxide (P O 4 10), and that in the presence of water, P O 4 10 is transformed to 3 H PO 4 (Beck and Unterberger, 2006), .Then, a fraction of 3 H PO 4 was condensed to form H P 2 4 7 O and reacted with metallic particles (K, Ca, Mg) to form pyrophosphates (e. g., K P 4 2 7 O, Mg P 2 2 7 O Ca and 2 P O 2 7 .Other The H part 3 of 4 PO reacted directly with the metallic particles to form a mixture of phosphate (e. g., K PO 3 4, 3 Mg (PO 4) 2 and 3 Ca (PO 4) 2) in small particles ( < 1 µm) and deposited on larger particles of biochar (0.01 - 1.0 mm) and Zhang Ninomiya, 2007 and Brown et al ., 2009). Because of the complexity of the reaction between 3 H PO 4 and metallic particles, hydrophosphate (e. g., K HPO 2 4,4 and 4 MgHPO CaHPO) and dihydric phosphate (e. g., KH PO 4 and 2 Mg (H PO 2 4.) 2.) of the metals were also present in this process, which were finally dehydrated to form pyrophosphates.

In the fast pyrolysis system, the temperature at outer layer of biochar was higher than that of inner layer. With an increase in retention time of biochar,The small P-containing particles deposited on the surface of larger biochar particles were dehydrated to form pyrophosphates, and there were more than pyrophosphates orthophosphate in the outer layer (Fig. 6. This can be used to partially explain the faster release rate of pyrophosphate in the initial 8 H, compared to that of orthophosphate. When biochar was added into water,The Ca Mg 2 and 2 were adsorbed onto the negatively charged functional groups to form a "Bridge" and provide the cation adsorption sites for anions. Hence, an increase in Ca Mg 2 and 2 would re-adsorb more phosphate. The occupation of active sites in cation bridge as well as on the surface of biochar by coexisting anions reduced the re-adsorption of phosphate released,and the enhanced P release. release of P The from biochar was influenced by many factors, besides those abovementioned.

Full - image size (32 K)
Fig. 6.
Distribution P species of biochar on surface. (a) Formation of orthophosphate and pyrophosphate; (b) Increased pyrophosphate in the outer layer of biochar surface; and (c) of Release orthophosphate and pyrophosphate from biochar in water.

Figure options 4. Conclusion
In summary, release from the P biochar to water was influenced by various factors, such as retention time, coexistence anions, and other nutrient elements. The P interaction between species and the surface of bichar are based on "ion bridge", thus the cations and anions in Solution could influence the migration of P.The environmental conditions can be adjusted to obtain the optimum P release parameters, for instance, to adjust the amount or speed of change P release by the concentration of the anions or other nutrient elements in the soil.massive The biochars produced derived from different crop residues and other biomass waste would be a potential P resource to mitigate the crisis if the P P leakage was avoided by optimization of P release parameters.


Acknowledgements The authors gratefully acknowledge financial support from 863 National Program (2012 AA 063608 - 01,National Key Technology R & D Program of the Ministry of Science and Technology (2012 BAJ B 08 00 ), and the Key Special Program S & T on the for the Pollution Control and Treatment of Water Bodies (No. ZX 07103 2012 - 001) .

Appendix A.Supplementary material