Mitigating Iron Toxicity by Using Rock Phosphate to Improve Rice Productivity

Iron toxicity is a major constraint to rice production, particularly in highly weathered soils of inland valleys in Sub-Saharan Africa where the rice growing area is rapidly expanding. This study aimed to improve the productiveness of iron toxicity sensitive’s rice fields as well as in the unsensitive fields by using local phosphate fertilizers. Eighteen (18) rice genotypes were been assessed in a split plot design in two areas: without iron toxicity and with iron toxicity. NPK, NK, Rock Phosphate, Triple super phosphate, Calcined phosphate and Acidulated phosphate were used as fertilizers. Data collection was focused on agronomic traits and yield (g/m2). The best fertilizers in the area without iron toxicity were NPK (820.2 g/m2) and triple super phosphate (751.7 g/m2). In the iron toxicity area, the best yields were performed by NPK (785.5 g/m2) and raw calcined phosphate (698.3 g/m2). Yet, the Accessions 15, Accessions 225, Accessions 226 and Accessions 270 were rainfed rice genotypes while CC109 A, HB 46 and HB 62 were low-land/irrigated rice genotypes. NPK, NK and acidulated phosphate fertilizers alleviate the best, iron toxicity in both sensitive and unsensitive rice fields.

Rare Earth Element Geochemistry of Phosphatic Rocks in Neoproterozoic Ediacaran Doushantuo Formation in Hushan Section from the Yangtze Gorges Area, South China

Phosphatic rocks are widely distributed in Neoproterozoic Ediacaran Doushantuo Formation in Yangtze Gorges Area, South China. In this study, rare earth element geochemistry of eight phosphatic rock samples from the Hushan Section has been studied. All the samples display typical hat-shaped REE patterns, moderate negative Ce anomalies（Ce/Ce＊=0.55 to 0.67）, slightly positive Eu anomalies（Eu/Eu＊=1.05 to 1.22） and low Y/Ho ratios（38.2±5.6）. The hat-shaped REE patterns indicate diagenetic alteration of the primary REE signatures, which coincides with detrital siliciclastic sources of REE based on the Y/Ho ratios. The degree of Negative Ce anomalies and positive Eu anomalies may have recorded the redox features of diagenetic fluids, suggesting an anoxic environment during the phosphogenesis processes in Neoproterozoic Ediacaran Doushantuo Formation, South China. The geochemical comparison between the Lower Phosphorite Layer and Upper Phosphorite Layer at Hushan indicates a greater degree of diagenesis occurred in the Upper Layer than the Lower one. Besides the terrigenous sources of REE, organic materials could have also played a role on the REE characteristics.

Effects of Acidiphilium cryptum on biosolubilization of rock phosphate in the presence of Acidithiobacillus ferrooxidans

The bioleaching of pyrite and biosolubilization of rock phosphate （RP） in 9K basal salts medium were compared by the following strains of an autotrophic acidophilic bacterium, Acidithiobacillus ferrooxidans, a heterotrophic acidophilic bacterium, Acidiphilium cryptum, and mixed culture of At. ferrooxidans and A. cryptum. The results show that A. cryptum is effective in enhancing the bioleaching of pyrite and biosolubilization of RP in the presence of At. ferrooxidans, although it could not oxidize pyrite and solubilize RP by itself. This effect is demonstrated experimentally that A. cryptum enhances a decrease in pH and an increase in redox potential, concentration of total soluble iron and planktonic part bacterial number in the broth during pyrite bioleaching processes by At. ferrooxidans. The mixed culture of At. ferrooxidans and A. cryptum leads to the most extensive soluble phosphate released at 30 °C. Pulp density exceeding 3% is shown to adversely influence the release of soluble phosphate by the consortium of At. ferrooxidans and A. cryptum. It is essential to add pyrite to the 9K basal salts medium for the biosolubilization of RP by the mixed culture of At. ferrooxidans and A. cryptum, and the percentage of soluble phosphate released is the greatest when the mass ratio of RP to pyrite is 1：2 or 1：3.

Excavation compensation and bolt support for a deep mine drift

To overcome large deformation of deep phosphate rock roadways and pillar damage,a new type of constant-resistance large-deformation negative Poisson’s ratio(NPR)bolt that can withstand a high prestress of at least 130 KN was developed.In the conducted tests,the amount of deformation was 200-2000 mm,the breaking force reached 350 KN,and a high constant-resistance pre-stress was maintained during the deformation process.A stress compensation theory of phosphate rock excavation based on NPR bolts is proposed together with a balance system for bolt compensation of the time-space effect and high NPR pre-stress.Traditional split-set rock bolts are unable to maintain the stability of roadway roofs and pillars.To verify the support effect of the proposed bolt,field tests were conducted using both the proposed NPR bolts and split-set rock bolts as support systems on the same mining face.In addition,the stress compensation mechanism of roadway mining was simulated using the particle flow code in three dimensions(PFC^(3D))-fast Lagrangian analysis of continua(FLAC^(3D))particle-flow coupling numerical model.On-site monitoring and numerical simulations showed that the NPR excavation compensation support scheme effectively improves the stress state of the bolts and reduces the deformation of the surrounding rock.Compared to the original support scheme,the final deformation of the surrounding rock was reduced by approximately 70%.These results significantly contribute to domestic and foreign research on phosphate-rock NPR compensation support technology,theoretical systems,and engineering practices,and further promote technological innovation in the phosphate rock mining industry.

Residual Effects of Phosphate Amendments on Rainfed Rice (Oryza sativa L.) Nutrition and Soil Properties in Three Agroecological Zones of Côte d’Ivoire

A study was conducted in Côte d’Ivoire to assess the after-effect of phosphate amendments on rice yields and soil properties. Eight types of amendments, composed of Moroccan phosphate rock (PRM) and triple superphosphate were tested in three agroecological zones over three consecutive years of cultivation. This study revealed that the application of Moroccan phosphate rock (PRM) and/or triple superphosphate (TSP) did not significantly affect soil cation exchange capacity (CEC) and organic carbon (Corg) content. However, there was a negative residual effect of PRM-rich treatments on soil pH and K and N content, but the impact varies depending on the characteristics of the soils studied. Furthermore, nutrient losses, notably nitrogen from −17.5 to −267.7 kg/ha and potassium (−0.1 to 0.7 kg/ha), were observed in all treatments. Only phosphorus showed a positive balance of +49.56 to +52 kg/ha in PRM-rich treatments. Treatment T3, composed of 80% RPM and 20% TSP, was the most effective in all zones, with a relative increase in grain yields of over 100% compared to the control. These results suggest that the input of natural phosphate rock can significantly improve rice yields and soil properties in the studied agroecological zones in Côte d’Ivoire.

Phosphorus release from phosphate rock and iron phosphate by low-molecular-weight organic acids

Low-molecular-weight(LMW) organic acids widely exist in soils, particularly in the rhizosphere. A series of batch experiments were carried out to investigate the phosphorus release from rock phosphate and iron phosphate by low-molecular-weight organic acids. Results showed that citric acid had the highest capacity to solubilize P from both rock and iron phosphate. P solubilization from rock phosphate and iron phosphate resulted in net proton consumption. P release from rock phosphate was positively correlated with the p K _a values. P release from iron phosphate was positively correlated with Fe-organic acid stability constants except for aromatic acids, but was not correlated with p K _a. Increase in the concentrations of organic acids enhanced P solubilization from both rock and iron phosphate almost linearly. Addition of phenolic compounds further increased the P release from iron phosphate. Initial solution pH had much more substantial effect on P release from rock phosphate than from iron phosphate.

Solubilization of Rock Phosphate in Liquid Culture by Fungal Isolates from Rhizosphere Soil

Rock phosphate （RP） is a low efficiency P fertilizer that is directly applied to the soil and can be solubilized by phosphate-solubilizing microorganisms （PSMs） in fermentation or soil conditions. This study investigated dynamic solubilization of 2 concentrations of rock phosphate in a liquid culture with different dosages of glucose by two fungal isolates,Aspergillus niger P39 and Penicillium oxalicum P66, from soybean and wheat rhizosphere soil. Although during the 20 day culture period A. niger P39 had a stronger ability to acidify the culture media than P. ozalicum P66, soluble P concentrations at glucose dosages of 30 and 50 g L^-1 with RP of 15 g L^-1 in the culture solution were much higher by P. oxalicum P66. The greater effectiveness of P. oxalicum P66 compared to A. niger P39 in the solubilization of RP was strongly associated with the production of organic acids. This study suggested that for RP solubilization the type rather than the concentration of PSM-produced organic acids was more important.

Phosphate rock reduces the bioavailability of heavy metals by influencing the bacterial communities during aerobic composting

Available information on the microbial mechanisms associated with heavy metal(HM)passivation during co-composting amended with phosphate rock(PR)remains limited.Thus,this study investigated the dynamic changes in bacterial communities and HM-fractions(Zn,Cu,Cd,Cr and Pb)during swine manure composting with maize straw,and ascertained the bacterial influence on HM-passivation.The results demonstrated that the addition of PR improved HM-passivation,especially for Zn and Cd,with their bioavailability factors(BFs)reduced by 247.41 and 176.25%,respectively.As for bacterial communities,the proportion of Firmicutes decreased,while the proportions of Proteobacteria,Bacteroidetes,DeinococcusThermus and Gemmatimonadetes increased in all treatments.PR significantly changed the primary bacterial phyla in the thermophilic phase.Bacteroidetes were the main bacterial component controlling the passivation of Zn,Cu and Cr,while Deinococcus-Thermus mainly regulated the mobility of Zn and Pb,and Proteobacteria only dominated the transformation among Cd-fractions.These results may provide a reference for the use of HM-passivation techniques during composting.

Phosphate Rock Fertilizer in Acid Soils: Comparing Phosphate Extraction Methods for Measuring Dissolution

Three phosphate extraction methods were used to investigate the dissolution, availability and transformation of Kunyang phosphate rock (KPR) in two surface acid soils. Dissolution was determined by measuring the increase in the amounts of soluble and adsorbed inorganic phosphate fractions, and did not differ significantly among the three methods. Significant correlations were obtained among P fractions got by the three extraction methods. Dissolution continued until the end of the 90 day incubation period. At the end of the period, much of the applied phosphate recovered in both soils were in the Al and Fe P or in the hydroxide and bicarbonate extractable inorganic P fractions. The dissolution of KPR in the two soils was also similar: increased addition of phosphate rock resulted in decreased dissolution. The similarity in the order and extent of dissolution in the two soils was probably due to the similarity in each soil of several factors that are known to influence phosphate rock dissolution, namely low CEC, pH, P level, and base status; and high clay and free iron and aluminum oxide contents. The results suggested that KPR could be an alternative P source in the long, if not the short, term in the soils, provided that those factors influencing P availability in the soils are not limiting.

Removal of Lead,Copper,Zinc and Cadmium from Water Using Phosphate Rock

Removal of Pb^2＋, Cu^2＋, Zn^2＋ and Cd^2＋ from aqueous solutions by sorption on a natural phosphate rock （FAP） was investigated. The effects of the contact time and initial metal concentration were examined in the batch method. The percentage sorption of heavy metals from solution ranges generally between 50% and 99%. The amount of sorbed metal ions follows the order Cu〉Pb〉Cd〉Zn. Heavy metal immobilization was attributed to both surface complexation of metal ions on the surface of FAP grains and partial dissolution and precipitation of a heavy metal-containing phosphate. The very low desorption ratio of heavy metals further supports the effectiveness of FAP as an alternative and low-cost material to remove toxic Pb^2＋, Cu^2＋, Zn^2＋ and Cd^2＋ from polluted waters.

Rock Phosphate Solubilization Mechanisms of One Fungus and One Bacterium

Many microorganisms can dissolve the insoluble phosphates like apatite. However, the mechanisms are still not clear. This study was an attempt to investigate the mechanisms of rock phosphate solubiliza-tion by an Aspergillus 2TCiF2 and an Arthrobacter1TCRi7. The results indicated that the fungus produced a large amount of organic acids, mainly oxalic acid. The total quantity of the organic acids produced by the fungus was 550 times higher than that by the bacterium. Different organic acids had completely different capacities to solubilize the rock. Oxalic acid and citric acid had stronger capacity to dissolve the rock than malic acid, tartaric acid, lactic acid, acetic acid, malonic acid and succinic acid. The fungus solubilized the rock through excreting both proton and organic acids. The rock solubilization of the bacterium depended on only proton.

Selective separation of silica from a siliceous-calcareous phosphate rock

Selective separation of silica from a siliceous-calcareous phosphate ore that had been sieved into different size fractions is investigated by a combination of chemical analysis,zeta potential measurement and FTIR and XPS techniques.Scrubbing is a better choice than flotation for removing silica from the coarse fractions.The P_2O_5 grade of the coarse fractions is increased to about 30%by scrubbing and the product yields are higher than those obtained by flotation.The silica in the fine fraction is separated by reverse flotation.An alkyl amine salt(DAH)is an effective collector and the P_2O_5 grade of the fine fraction can be increased by 7%to beyond 30%under acidic conditions.The higher zeta potential obtained using DAH suggests that it is more strongly absorbed onto the ore particles than the other cationic collectors. FTIR and XPS results confirm physical absorption of the cationic collector onto the ore surface.They also indicate that calcite is dissolved at low pH values,which increases the Si concentration on the ore surface.

Bio-decomposition of rock phosphate containing pyrites by Acidithiobacillus ferrooxidans

Leaching soluble phosphorus from rock phosphate containing pyrites by Acidithiobacillus ferrooxidans (A.f.) is feasible, and the reaction mechanism is as follows. Pyrites are oxidized by A.f. to produce H_2SO_4 and FeSO_4; the rock phosphate is decomposed by H_2SO_4, forming soluble phosphorus compounds; and Fe2+ from FeSO_4 is oxidized to Fe^3+, providing energy for the growth of A. f.. In this process, as H_2SO_4 is produced in the reaction, an acidic condition in the culture medium is formed, which benefits the growth of A. f. and aids both continuous oxidation of pyrites and leaching of soluble phosphorus from rock phosphate. The fraction of phosphorous leached can reach the largest in the presence of 1.0 g/L Fe^3+, 200 mg/L Mg^2+ and 400 mg/L NH_4^+. The optimal technological parameters on the fraction of phosphorous leached are as follows: the volume fraction of inocula of A. f., the mass ratio of pyrites to rock phosphate and the pH value are in ranges of 5%-25%, 3:1-5:1 and 1.8-2.2, respectively.

Application of Ground Phosphate Rock to Dimmish the Effects of Simulated Acid Rain on Soil Properties

The effects of simulated acid rain retained in soil on the properties of acid soil and its diminishing by application of ground phosphate rock were investigated by using the sorption method. Results show as follows: (1) For yellow brown soil, the effect of simulated acid rain on the properties of soil with a pH value of 5.9 was relatively small, except a great quantity of acid rain deposited on it. (2) For red soil, the effect of simulated acid rain on the properties of soil was significant. With the increase of the amount of acid deposition, the pH value of soil was declined, but the contents of exchangeable H+, Al3+ and Mn2+ and the amount of SO42- retention were increased. (3) Many properties of acid soils could be improved by applying ground phosphate rock. For example, pH value of soils and the amounts of available P and exchangeable Ca2+ and Mg2+ were increased, and the amounts of exchangeable H+ and Al3+ and SO42- retained was reduced. The application of ground posphate rock could effctively dimmish the pollution of acid rain to soil.

Bioleaching of soluble phosphorus from rock phosphate containing pyrite with DES-induced Acidithiobacillus ferrooxidans

The effects of Acidithiobacillus ferrooxidans(At. f) mutated with diethyl sulfate(DES) as a mutagen on the bioleaching of soluble phosphorus(P) from rock phosphate(RP) were investigated. The results show that the oxidative activity of At. f is greatly improved by 1.0%(volume fraction) of DES. Correspondingly,the highest leaching rate of soluble P is also obtained to be 14.9% by the At. f mutated,which is 85.8% higher than that of the adapted At. f without mutation. In addition,the SEM images are significantly performed that the corrosion of RP residue surfaces leached by 1.0% DES-induced At.f is much worse than that of leached by the adapted At. f. All the above indicate that the leaching efficiency of soluble P from RP with pyrite can be greatly improved by using DES-induced At. f to a certain extent.

Agronomic Effectiveness of Partially Acidulated Phosphate Rock

Laboratorial incubation and field experiments were conducted on soils ranging in texture from sandy loam toclay and in PH from 3 .6 to 9.0 to determine the agronomic effectiveness of single superphosphate (SSP), fused magne-sium phosphate (FMP)and partially acidulated phosphate rock (PAPR)on 8 field crops. The results showed that thepottern of available P released from SSP was fixing -releasing-fixing-steady state, while that of PAPR was shortlyfixing-slowly releasing-fixing-steady state And the PAPR . SSP and FMP were equally effective as judged by yield, Puptake by plants and extractable P in soils after crop harvesting. The PAPR used as basal fertilizer was more effectivethan that as top dressing, and its residual effect was also obvious.

Effect of Lanthanum on Solubilization of Rock Phosphate in Liquid Culture by Aspergillus Niger and Penicillium Oxalicum

Rock phosphate (RP) is a low efficient P fertilizer when directly used in the soil. Phosphate-solubilizing microorganisms (PSMs) can solubilize RP in fermentation or soil condition. The effect of different concentration of lanthanum (La) on the solubilization of RP was investigated by two isolates of phosphate-solubilizing fungi (PSF) Aspergillus niger P39 and Penicillium oxalicum P66 in liquid culture. Experimental results show that relatively higher concentration of La in the culture solution inhibites fungal growth and delays RP solubilizing activity of two isolates. This inhibitory effect of La on RP solubilization varies with PSF (isolate P66 is more sensitive to La than P39 in this experiment). Comparing the pH value of culture media with soluble P content as affected by La application, only within individual isolate not different isolates the negatively significant relationship was observed.

Distribution of Phosphorus in Minjingu Phosphate Rock and Ikutha Rock Samples

Minjingu Phosphate Rock （MPR） from Northern Tanzania and the Ikutha Phosphate Rock （IPR） found in Central-Southeast Kenya are well documented as potential sources of phosphorous （P） available in East Africa. On-farm trials in phosphate-deficient soils in Western Kenya demonstrated MPR to be as effective as triple superphosphate （TSP） - 20% P, at equal P rates. The aim of this work is to determine the distribution of phosphorus in these phosphate rocks （PRs）. The different phosphorus fractions were extracted using the modified Williams extraction procedure and analysis carried on a UV/VIS spectrometer （SHIMADZU UV-220-02 and NOVASPEC II）. The analysis showed that the most abundant form of phosphorus in the phosphate rocks was the Inorganic Phosphorus （IP） contributing 74.20% of total phosphorus （TP） for Minjingu, and 83,28% of total phosphorus for Ikutha phosphate rock.

Agronomic Potential of Partially Acidnlated Rock Phos－phates in Acid Soils of Subtropical China

A glasshouse experiment was conducted to evaluate the agronomic potential of four partially acidulatedrock phosphates (PARP) in three representative soils sampled from subtropical China. The PARPs weremanufactured by attacking a moderately reactive phosphate rock either with sulfuric acid alone or withcombination of sulfuric and phosphoric acids at 30 or 60 percent of acidulation. Shoot dry weight and Paccumulation of six successive cuttings of ryegrass were used to compare the agronomic potential of thesefertilizers with that of the raw rock phosphate (RP) and monocalcium phosphate (MCP). Results indicatedthat the effectiveness of various phosphates was determined both by the solubility of the phosphates andby the acidity and P-fixing capacity of the soils. The higher the watersoluble P contained, the better theeffectiveness of the fertilizer was. Although plant P accumulation of PARP treatments was constantly lowerthan that of MCP treatment, some PARPs could still get a dry matter production similar to that of MCPtreatment. PARP SP60, which was acidulated with a mixture of sulfuric acid and phosphoric acid at 60percent of acidulation and contained the highest soluble P, was as effective as MCP in terms of dry matterproduction on all the soils. 560 and C1, which were both acidulated with sulfuric acid with the formerat 60 percent of acidulation and the latter at 30 percent but with a further addition of monoarninoniumphosphate, were more than 80 percent as effective as MCP. Raw RP also showed a reasonable effectivenesswhich increased with soil acidity. It was suggested from the study that some of these PARPs could beexpected to have a comparable field performance as soluble P fertilizers in the acid soil regions.

Growth Characteristics of Mixed Bacteria and Its Solubilizing Effect on Low-grade Phosphate Rock

In this paper, the growth characteristics of Acidithiobacillus ferrooxidans （At.f） and Acidithiobacillus thiooxidans （At. f） in mixed culture has been studied, explored mixed bacteria phosphate solubilization effect, from a kind of low-grade phosphate rock. The results show that mixed bacteria has strong ability to produce acid, and have stronger oxidation activity to energy source -Fe^2＋. Mixed bacteria can significantly increase the rate of phosphate solubilization from phosphate rock in low concentration pulp. It goes against mixed bacteria reproduction when pulp concentration increased, makes phosphate solubilization rate decreased.