『Abstract
Background, aim and scope The production of alumina involves
its extraction from bauxite ore using sodium hydroxide under high
temperature and pressure. This process yields a large amount of
residue wastes, which are difficult to revegetate due to their
inherent hostile properties - high alkalinity and sodicity, poor
water retention and low nutrient availability. Although phosphorus
(P) is a key element limiting successful ecosystem restoration,
little information is available on the availability and dynamics
of P in rehabilitated bauxite-processing residue sand (BRS). The
major aim of this experiment was to quantify P availability and
behaviour as affected by pH, source of BRS and d-ammonium phosphate
(DAP) application rate.
Materials and methods This incubation experiment was undertaken
using three sources of BRS, three DAP application rates (low,
without addition of DAP; medium, 15.07 mg P and 13.63 mg N of
DAP per jar, 100 g BRS; and high, 30.15 mg P and 27.26 mg N per
jar, 100 g BRS), and four BRS pH treatments (4, 7, 9 and 11 (original)).
The moisture content was adjusted to 55％ water holding capacity
and each BRS sample was incubated at 25℃ for a period of 119 days.
After this period, Colwell P and 0.1 M H2SO4 extractable P in BRS were determined. In addition,
P sequential fractionation was carried out and the concentration
of P in each pool was measured.
Results and discussion A significant proportion (37％ recovered
in Colwell P and 48％ in 0.1 M H2SO4
extraction) of P added as DAP in BRS are available for plant use.
The pH did not significantly affect 0.1 M H2SO4 extractable P, while concentrations of Colwell
P in the higher initial pH treatments (pH 7, 9 and 11) were greater
than in the pH treatments. The labile fractions (sum of NH4Cl (AP), bicarbonate and first sodium hydroxide
extractable P (N(I)P)) consisted of 58-64％ and 70-72％ of total
P in the medium and high DAP rate treatments, respectively. This
indicates that most P added as DAP remained labile or moderately
labile in BRS, either in solution, or in adsorbed forms on the
surface of more crystalline P compounds, sesquioxides and carbonate,
or associated with amorphous and some crystalline Al and Fe hydrous
oxides. In addition, differences in hydrochloric acid extractable
P and the residual-P fractions among the treatments with and without
DAP addition were relative small comparing with other P pools
(e.g., NaOH extractable P pools), further indicating the limited
capacity of BRS for fixing P added in Ca-P and other most recalcitrant
forms.
Conclusions P availability in the original BRS without
addition of DAP was very low, mostly in recalcitrant form. It
has been clearly demonstrated that significant proportions of
P added as DAP could remain labile or moderately labile for plant
use during the rehabilitation of bauxite-processing residue disposal
areas. There was limited capacity of BRS for fixing P in more
recalcitrant forms (e.g., Ca-P and residual-P). Concentrations
of most P pools in BRS increased with the DAP application rate.
The impact of the pH treatment on P availability varied with the
type of P pools and the DAP rate.
Recommendation and perspectives It is recommended that
the development of appropriate techniques for more accurate estimation
of P availability in BRS and the quantification of the potential
leaching loss of P in BRS are needed for the accurate understanding
of P availability and dynamics in BRS. In addition, application
of organic matters (e.g., biosolids and biochar, etc.) to BRS
may be considered for improving P availability and buffering capacity.
Keywords: Bauxite-processing residue sand; Di-ammonia phosphate;
Phosphorus (P) availability; Chemical fractionation; H2SO4 extractable P; Colwell P』
1. Introduction
2. Materials and methods
2.1. Experimental setup
2.2. Chemical analysis
2.3. Statistical analysis
3. Results and discussion
3.1. Available P in BRS
3.2. Phosphorus fractions from sequential fractionation
4. Conclusions and recommendation
Acknowledgement
References
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| 1.000 gの風乾土壌 | 30 mlの1M NH4Clを加え、16時間振とう、10000 rpm（回転数／分）で10分間遠心分離 | Solution-P（溶液-P）（AP） |
| 残渣 | 30 mlの0.5M NaHCO3を加え、16時間振とう、10000 rpmで10分間遠心分離 | BPi & BPo |
| 残渣 | 30 mlの0.1M NaOHを加え、16時間振とう、10000 rpmで10分間遠心分離 | N(I)Pi & N(I)Po |
| 水洗（30 mlのH2Oを加え、4時間振とう、10000 rpmで10分間遠心分離、上澄み液廃棄） | ||
| 残渣 | 30 mlの1M HCｌを加え、16時間振とう、10000 rpmで10分間遠心分離 | HPi |
| 上記のように水洗 | ||
| 残渣 | 30 mlの0.1M NaOHを加え、16時間振とう、10000 rpmで10分間遠心分離 | N(II)Pi & N(II)Po |
| 上記のように水洗 | ||
| 残渣 | 脱イオン水で温浸管（digestion tube）へ移し、60℃で乾燥、8 mlの濃硝酸（HNO3）と4 mlのHCｌO4を用いて温浸 | Residual-P（残渣-P） |