Phosphate Concentration In Solution Research Articles

REE ultra-rich karst bauxite deposits in the Pedernales Peninsula, Dominican Republic: Mineralogy of REE phosphates and carbonates

Karst bauxites have recently received renewed attention for their potential as non-conventional REE sources. Karst bauxites from the Pedernales Peninsula in the Dominican Republic stand among the world’s richest in REE. Bauxite ore from two deposits from this bauxite district, Aceitillar and El Turco, have been selected for this study due to their outstanding REE contents and contrasting mineralogy. REE (La to Lu) contents in Aceitillar, range from 0.07 to 0.16 wt%, and Y from 0.01 to 0.13 wt%, whereas El Turco contains between 0.28 and 1.40 wt% REE, and 0.33 to 1.48 wt% Y. The characterisation of REE mineralisation was performed through powder and monocrystal XRD, SEM-EDS, and EMP analyses. REE phosphates and carbonates reveal textural features that suggest significant REE mobilisation and re-deposition within the bauxite profile. The identified REE minerals can be classified into: i) primary monazite(-Ce) and minor monazite(-La); ii) secondary Y- and Nd-dominant phosphates; and iii) secondary Gd- and Nd-carbonates of the (hydroxyl)bastnäsite group. While monazites are ubiquitous in the two studied deposits, secondary phosphates are predominant in El Turco while secondary carbonates are exclusive of Aceitillar. This contrasting mineralogy is explained by the total concentration of carbonate and/or phosphate in the karst bauxite groundwater solutions. REE phosphates are the most stable phases at [CO32−]total/[PO43−]total ≤ 2; whereas REE carbonates are stable at near neutral pH when the total aqueous carbonate concentration is two orders of magnitude higher than that of phosphate. Results of this investigation contribute to a better understanding of the formation REE minerals in the supergene environment and can be applied in REE separation methods.

Modification of sand with Fe-Zn oxides: an alternative strategy to improve adsorption of phosphate from artificial wastewater treatment

ABSTRACT In this work, Fe-decorated quartz sand (FS), Fe-Mn bimetallic cation-decorated quartz sand (FMS) and Fe-Zn bimetallic cation-decorated quartz sand (FZS) were synthesised from ordinary quartz sand (QS). Iron, iron-manganese and iron-zinc oxides were stably formed on the surfaces of FS, FMS and FZS, respectively. The specific surface area of FZS (1.0497 m2/g) increased to more than 320% against that of QS (0.2482 m2/g). The obtained samples were evaluated for the removal of phosphate from artificial wastewater. Parameters that can affect adsorption process include solution phosphate concentration, pH and retention time, which were investigated by bath adsorption experiments. Under the optimal experimental conditions (pH value 4.0, initial concentration of phosphate 15 mg/l, temperature 25°C, retention time 150 min and adsorbent dose 5 g), the removal efficiency of phosphate by FS was higher than that of QS, FS and FMS and the maximum phosphate adsorption capacity (qmax) provided by FZS is 0.18 mg/g. Furthermore, the kinetics of phosphate adsorption fit well with the pseudo-second-order model, indicating that adsorption of phosphate on the Fe-Zn co-decorated quartz sand occurred through chemisorption, and the Langmuir adsorption isotherm model (R2 = 9944) is more suitable for adsorption capacity prediction than the Freundlich adsorption isotherm model (R2 = 0.9427). The results show that quartz sand can be modified effectively, which has great practical application potential in water treatment.

Phosphate and buffer capacity effects on biomimetic carbonate apatite

With the increasing use of carbonated apatite (CAp) in biomedical devices, it has become necessary to understand how this thermodynamically unstable mineral interacts with varying surrounding body fluids. Despite existing knowledge about the evolution of other calcium phosphates in bio-like fluids, it is unknown how CAp reacts in these solutions. Therefore, our goal was to determine how solution phosphate concentration and the buffer capacity (BC) affects CAp dissolution/recrystallization. To do so, CAp powder was first synthesized through an aqueous precipitation reaction and then exposed to one of the following solutions for 3 days: (1) 0 mM PO4, (2) 8 mM PO4, (3) 16 mM PO4, (4) low BC, or (5) high BC. Afterwards, the powders were analyzed for mass loss, composition via Raman, crystal structure via XRD, and size via TEM. The solutions were evaluated for Ca, P, Na, and K through ICPOES. Our results suggest that increased phosphate in the solution, regardless of BC, created larger, more crystalline CAp crystals, indicating crystal maturation. In addition, the crystals had fewer carbonate substitutions and more phosphate ion uptake from the solution after pH equilibrium. This data offers insight on how CAp in biomaterials may mature and change composition and material properties in the body after implantation.

Phosphate Limitation Susceptibility in Saccharomyces Cerevisiae

Phosphate is a protein vital for all organismal bodies and is a resource bacteria compete for. Bakers yeast activity under several concentrations of phosphate and an alkaline solution was observed through absorbance spectroscopy as a means of measuring the various levels of inhibition from several varying concentrations. This was expected to show increased bacterial activity to increased phosphate concentration. Under higher concentrations of phosphate, Saccharomyces Cerevisiae became inhibited. This study focused on determining if the activity of the yeast changes based on the varying concentrations of phosphate solutions.

Passivation behaviour of mild steel embedded in magnesium potassium phosphate cement-calcium sulphoaluminate cement blended paste

• Passivity of mild steel embedded in MKPC-CSA blended paste were investigated. • CSA addition significantly influences the degree of passivity. • Passivity increases with increased CSA addition and 30% CSA addition leads to a much higher passivity. • 30 % CSA addition benefits the precipitation of phosphate ions and formation of Fe 2+ oxide in passive film. This study did a pioneer work focused on the passivation of mild steel embedded in magnesium potassium phosphate cement (MKPC)-calcium sulphoaluminate cement (CSA) blended paste via electrochemical measurements and materials characterization techniques. Results showed that 30 % CSA addition in MKPC leads to a passivity of mild steel much higher than that in Portland cement (PC) paste. The passivity of mild steel increased with an increase in CSA content in MKPC paste due to an increase in pH and phosphate concentration in pore solution. The formation of iron phosphate and Fe 2+ oxide in passive film of MKPC-30 %CSA contributes to its highest passivity.

Synthesis and Characterization of 2D Magnesium Oxide Nanoflakes: A Potential Nanomaterial for Effective Phosphate Removal from Wastewater

AbstractPhosphate containing untreated wastewater, discharged into water bodies, can cause eutrophication, leading to harmful effects on the ecosystem and human health. This study focuses on a simple, low‐cost, and novel approach towards removing excess phosphate ions from aqueous solutions by adsorbing on onto two‐dimensional (2‐D) magnesium oxide nano‐flakes (MONFs). The phosphate removal efficiency was tested with different concentrations of phosphate solutions (2–25 mg L−1), pH levels (3–11), adsorbent dosages (0.025‐0.250 g), and contact times (10‐50 min). The maximum phosphate removal percentage of 100 % was obtained with 50.0 mL of 3 mg L−1 phosphate solution using 0.125 g of the synthesized MONFs with a phosphate absorption capacity of 29.9 mg g−1. Moreover, the adsorption data fit with the Freundlich isotherm, with an R2 value of 0.952. The adsorption kinetic data follow the pseudo‐second‐order model, with an R2 value of 0.995, suggesting that the adsorption process is chemisorption.

Biochemical Fulvic Acid Modification for Phosphate Crystal Inhibition in Water and Fertilizer Integration.

Biochemical fulvic acid (BFA), produced by organic wastes composting, is the complex organic matter with various functional groups. A novel modified biochemical fulvic acid (MBFA) which possessed stronger chelating ability had been synthesized by the grafting copolymerization of BFA and acrylic acid (AA). Results showed that MBFA effectively inhibited the crystallization of calcium phosphate and increased the concentration of phosphate in water solution. The optimum reaction conditions optimized by Box–Behnken design and response surface methodology were reaction temperature 69.24 °C, the mass of monomer to fulvic acid ratio 0.713, the initiator dosage 19.78%, and phosphate crystal-inhibition extent was 96.89%. IR spectra demonstrated AA was grafted onto BFA. XRD data and SEM images appeared the formation and growth of calcium phosphate crystals was effectively inhibited by MBFA.

Inferential control of the phosphate concentration in hydroponic systems via measurement of the nutrient solution's pH-buffering capacity

Urban hydroponics is expanding on a global scale. This provides environmentalists with an ideal opportunity to couple sustainability principles to the development of the sector. A primary concern in hydroponics is the generation of large amounts of nutrient laden wastewater. Unlike conventional agriculture, the water effluent typically exits the urban farm via a dedicated outlet, where water quality can be monitored and regulated. It is therefore imperative to develop processes in which the quality of the exit water is part of the design objective. Minimisation of nitrogen and phosphorous in the effluent is key in this regard. This study presents an affordable technique to control phosphate levels in a hydroponic unit. The technique relies solely on continuous pH measurement from which the pH-buffering capacity of the nutrient solution is calculated. The pH-buffering capacity is then used as an inferential measurement to control the phosphate concentration in solution. This concentration can then be controlled at significantly lower levels and thereby reduce phosphate spillage proportionally. Experiments were performed in which the phosphate concentration was controlled at 1 ±0.08 mM (representing standard protocol), 0.2 ±0.03 mM and 0.1 ±0.03 mM. No significant variation in plant growth rate or leaf mass fraction was observed in the runs with lower phosphate concentrations, suggesting that optimal growth is possible at phosphate levels ten times lower than conventional practice. Since the phosphate concentration in the hydroponic outlet is directly proportional to the load of phosphate spillage, the results are encouraging from a nutrient pollution perspective.

Synthesis, characterization and phosphate adsorption of (Fe, Al, Cu) oxit/bentonite nanocomposite

(Fe, Al, Cu) oxide/bentonite nanocomposite – FACB, was simply prepared by co-precipitation of salts of Fe, Al and Cu, which were impregnated previously in the exfoliated bentonite suspension. Characterization of the FACB is performed by X-ray diffraction, Fourier transform infrared spectrometry, Field emission scanning electron microscopy, Energy-dispersive X-ray spectroscopy, Nitrogen adsorption isotherm, and Thermal analysis. The adsorption behavious of phosphate ion on the FACB was assessed. The material has a good ability of phosphate adsorption with high adsorption rate and adsorption capacity of 55.87 mg P/g at equilibrium concentration of phosphate solution of 24.13 mg/l.

Effect of Bacillus spp. on Lettuce Growth and Root Associated Bacterial Community in a Small-Scale Aquaponics System

The integration of probiotics in aquaponics systems is a strategy for mitigating environmental impacts and for promoting sustainable agriculture. In order to understand the role of probiotics, we investigated the effect of a commercial probiotic mixture of Bacillus subtilis and B. licheniformis on the growth of lettuce (Lactuca sativa L.) under deep-water culture integrated with Mozambique tilapia (Oreochromis mossambicus). We determined plant growth, water quality parameters, and leaf mineral analysis, and assessed the influence of a probiotic mixture on the microbiota. Bacterial communities were analyzed by high-throughput 16S rRNA gene sequencing. Compared to the control systems, the addition of the probiotic Bacillus significantly increased the concentration of nitrate and phosphate in deep water culture solution, which contributed to improved lettuce growth. In both the growth trials, the Fv/Fm, the mean shoot dry weight, and the mean fresh weight of the harvested shoots from the Bacillus treatment were significantly higher than those observed for the control plants. Higher concentrations of phosphorus, potassium, and zinc in the lettuce leaves were found in systems that received the Bacillus. Although differences were observed at the phylum level, Proteobacteria and Bacteroidetes were predominant in both the Bacillus-treatment and the control systems. At the genus level, however, the communities present in the two types of systems were heterogeneous with Bacillus-treated systems, containing significantly higher numbers of Chryseobacterium, Bacillus, Nitrospira, Polynucleobacter, and Thermomonas. The results indicate that Bacillus supplementation can effectively alleviate nutrient deficiencies, improve water quality, and modify the composition of bacterial communities in aquaponics systems.

Development of carbonate-associated phosphate (CAP) as a proxy for reconstructing ancient ocean phosphate levels

Phosphorus is considered the ultimate limiting nutrient in the oceans over geological timescales. Phosphate (PO43-) availability consequently exerts control on the global carbon cycle and atmospheric/oceanic redox conditions over million-year timescales. Despite its importance, there are no established tools that can directly and continuously reconstruct oceanic phosphate concentrations through time. Here, we report a new approach to carbonate-associated phosphate (CAP) extraction and a series of experiment-based constraints for using CAP as a tool for reconstructing ancient oceanic phosphate concentrations. Experimental work shows that phosphate is incorporated into carbonate at various concentrations as a function of solution phosphate concentration, pH, temperature, and carbonate mineralogy. It is recommended here that in order to selectively extract CAP, carbonate sediments should be partially leached in order to avoid contamination from non-carbonate phases. Analyses of recent and ancient carbonates indicate that CAP values may shift during neomorphic aragonite-to-calcite transformations and secondary alteration. Diagenetic carbonate concretions in the organic- and phosphorus-rich Monterey Formation yield elevated CAP values that correlate with indicators of significant organic matter oxidation; however, this pattern was not observed for geologically young, weakly altered carbonates in the Marion Platform (north-eastern Australian shelf). These observations suggest CAP can yield reliable information on secular variation in oceanic phosphate concentrations and semi-quantitative reconstructions, if samples are characterised mineralogically and screened for secondary alteration.

Hydrothermal synthesis of hydroxyapatite coating on the surface of medical magnesium alloy and its corrosion resistance

The early corrosion control of biomedical magnesium alloy is an important measure to determine its good performance during implantation into human body. The deposition of calcium phosphate biological coating is the most effective solution at present. In this paper, hydroxyapatite (HAP) coating was hydrothermal synthesized on the surface of AZ31B magnesium alloy, and the influence mechanism of hydrothermal synthesis temperature, time and solution concentration was investigated. The synthesis conditions and deposition mechanism of hydroxyapatite coating without DCPA (CaHPO4) were proposed. The surface morphology of the coating was observed by field emission electron scanning microscope (FESEM). The types and contents of microelements in the material were analyzed by energy disperse spectroscopy (EDS). Fourier transform infrared spectroscopy (FTIR) was used to analyze the functional group information of the coating surface. The corrosion resistance of different experimental groups was studied by electrochemical test. The results showed that when the calcium phosphate solution concentration was 0.1 ​mol/L and the calcium/phosphorus ratio was 1.67, the coating had better morphology structure and corrosion resistance, and the calcium/phosphorus ratio of HAP crystals reached 1.58, the epit of the prepared AZ31B-HAP coating by bare metal increased from −1.51 ​V to −1.18 ​V, the impedance value reached 1.0 ​× ​105 ​Ω▪cm2, and the early corrosion of magnesium alloy substrate was effectively delayed.

A Co-Nanoparticles Modified Electrode for On-Site and Rapid Phosphate Detection in Hydroponic Solutions.

Conventional strategies for determining phosphate concentration is limited in efficiency due to the cost, time, and labor that is required in laboratory analysis. Therefore, an on-site and rapid detection sensor for phosphate is urgently needed to characterize phosphate variability in a hydroponic system. Cobalt (Co) is a highly sensitive metal that has shown a selectivity towards phosphate to a certain extent. A disposable phosphate sensor based on the screen-printed electrode (SPE) was developed to exploit the advantages of Co-nanoparticles. A support vector machine regression model was established to predict the concentration of phosphate in the hydroponic solutions. The results showed that Co-nanoparticles improve the detection limit of the sensor in the initial state. Meanwhile, the corrosion of Co-nanoparticles leads to a serious time-drift and instability of the electrodes. On the other hand, the coefficient of variation of the disposable phosphate detection chip is 0.4992%, the sensitivity is 33 mV/decade, and the linear range is 10−1–10−4.56 mol/L. The R2 and mean square error of the buffer-free sensor in the hydroponic solution are 0.9792 and 0.4936, respectively. In summary, the SPE modified by the Co-nanoparticles is a promising low-cost sensor for on-site and rapid measurement of the phosphate concentration in hydroponic solutions.

Effect of phosphate treatment on interfacial properties of poplar fiber/high-density polyethylene composites

Poplar fiber was treated with phosphate solution as a modifier and then wood fiber/high-density polyethylene (HDPE) degradable composite was prepared by melt blending with HDPE. The effects of phosphate solution concentration on tensile strength and flexural strength of composites were investigated. The surface morphology of phosphate-treated poplar fibers was observed by scanning electron microscopy. The results show that the phosphate treatment increases the surface roughness of the poplar fiber, increases the strength of the single fiber, and effectively improves the mechanical adhesion to the HDPE matrix. However, when the phosphate concentration is too large, the density of the cellulose molecular chains is lowered, and the mechanical properties of the whole fiber are lowered. When the concentration of phosphate solution is 3%, the treatment time is 4 h, and the treatment temperature is 60°C, the tensile properties, bending properties, and water resistance of poplar fiber/HDPE composites are the best.

In-situ study of the kinetics of phosphoric acid interaction with calcite and fluorapatite by Raman spectroscopy and flotation

In the reverse anionic flotation of phosphate ores using phosphoric acid, it is often suggested that a selective surface passivation of the phosphate minerals by calcium phosphate occurs. Several calcium phosphate species have been proposed in the literature for this surface passivation. In this study, in-situ Raman spectroscopy was used to monitor as a function of time the interaction of phosphoric acid with calcite and fluorapatite at a fixed pH of 4.5 or at fixed phosphoric acid concentrations in order to identify what species have formed in conditions similar to those used in flotation. X-ray photoelectron spectroscopy was also used to confirm and identify more clearly the species formed at the minerals surface. Although a calcium phosphate (1:1) species was observed on both minerals, its presence on calcite was highly dependent on phosphoric acid concentration and pH as the latter controls both calcium dissolution and calcium phosphate precipitation. The results of mineral flotation have confirmed the importance of phosphate concentration in solution, originating from phosphoric acid addition and/or mineral dissolution, in the formation/precipitation of calcium phosphate which can turn on or off the flotation of calcite or fluorapatite, or both.

Effects of the iron oxidation and precipitation processes on the arsenate sorption and coprecipitation

The main aim of this study was to assess the effects of ferrous iron oxidation, hydrolysis and precipitation of the ferric iron on the mechanisms of arsenate removal from acid mine drainage. The study was realized at the pH range 2,0 – 6,5. H2O2 was the oxidant used in the chemical test. A mixed culture of mesophilic iron-oxidizing chemolithotrophic bacteria (Acidithiobacillus ferrooxidans, Leptospirillum ferroxidans) carried out the ferrous oxidation in the biological test. NaOH was used as an alkalizing agent which triggered the ferric iron hydrolysis and precipitation. The results showed that the total content of retained arsenic by ferric iron hydrous oxides and its speciation as geochemical fractions depended on the iron and phosphate concentrations in acid solution. The results showed that phosphate concentration lower than 6 mg/ L limited the ferrous iron oxidation rate. At the tested experimental conditions, arsenic sorption by formed ferric iron hydrous oxides was the main mechanism for its removal from acid mine drainage, as the ratio between iron and phosphate determined the proportions between the geochemical fractions of scavenged arsenic.

Removal of Phosphate from Aqueous Solutions Using Chemically Synthesized Vaterite Polymorph of Porous Calcium Carbonate Nanoparticles under Optimized Conditions

Eutrophication is one of the most adverse impacts of nutrient contamination of water bodies where the phosphate is considered to be the primary limiting factor. The vaterite polymorph of porous calcium carbonate nanoparticles (VPCCNPs) were synthesized and used to remove orthophosphate ions in water. In this study, the VPCCNPs were synthesized chemically, using calcium acetate and sodium bicarbonate in a water-ethylene glycol media, at a temperature of 100°C, in a reaction time of 24 hours. Synthesized nanoparticles were characterized by X-ray diffractometry to confirm that the crystalline phase of calcium carbonate formed is spherical vaterite polymorph. Scanning electron microscopy coupled with energy dispersive X-ray analysis further confirms the spherical shape of the vaterite nanoparticles and the presence of only calcium, carbon, and oxygen thus showing high purity of the synthesized calcium carbonate nanoparticles. The dynamic laser light scattering-based particle size analysis (DLS) shows the average particle size to be 25.5 nm. The Fourier transform infrared spectroscopy was used to find functional groups before and after the adsorption of phosphate by vaterite nanoparticles. The phosphate removal efficiency of synthesized nanoparticles was tested with different concentrations of phosphate solutions (2–80 mg/L), pH levels (5–12), adsorbent dosages (0.025–0.250 g), and contact times (5–120 min). Ion chromatography was used to analyse the phosphate concentrations in water samples. The maximum phosphate removal percentage of 100% was obtained with 50 mL of 2 mg/L phosphate solution and 0.15 g of the synthesized nanoparticle. Adsorption data were well fitted with the Langmuir adsorption isotherm model and the pseudo-second-order kinetic model with R2 of 0.99 and 0.98 (rate constant -0.083 g g-1 min-1), respectively. The presence of F−, NO3−, and SO42− has no effect on phosphate adsorption since 100% phosphate removal is obtained in the presence of these ions. Furthermore, the particle shows a 100% removal of orthophosphate ions available in eutrophic water regardless of the presence of many other ions in natural water bodies. The study presents a viable option for removing excess phosphate in natural water to desirable levels as a means for controlling eutrophication.

Oxidized Black Phosphorus Nanosheets as an Inorganic Antiresorptive Agent

Black phosphorus (BP) is a newly discovered two-dimensional material that has promising applications from bioelectronics to biomedicine. However, facile oxidation of BP leads to changes in surface ...

Phosphate Sorption onto Structured Soil

Soil–phosphorus interactions are frequently studied employing the slurry technique, in which soil samples are intensively mixed with phosphate solutions of various concentrations. The result of such experiments is a “phosphate sorption potential” because the thorough mixing of soil and phosphate solution as obtained by overhead or horizontal shaking of the slurry would probably not occur under natural conditions, especially if the soil is structured. Here, we wanted to test the impact of soil structure on phosphorus (P) removal from aqueous solution. Soil aggregates of a defined size class were prepared by carefully sieving the soil. The soil aggregates were individually wrapped in an inert fabric and placed on a sieve, which was lowered into a basin containing a phosphate solution of a given concentration. The decrease of the phosphate solution concentration with time was registered at fixed intervals, and adsorbed amounts were quantified by differences between initial concentrations and concentrations at the time of sampling. Pre-tests on fine earth revealed that sorption was more pronounced in the classical slurry batch experiment than in the approach used in this study. Differences between methods were more pronounced at lower initial phosphate concentrations. The increase in P sorption in the classical batch experiment continued over 24 h to 140 mg kg−1, while the adsorbed P amount remained constant (64 mg kg−1) after 6 h in the diffusion experiment. Interestingly, it was observed that the sorption onto soil aggregates was elevated as compared to unstructured fine earth. The sorption capacity of aggregates was approximately one third higher than that of the fine earth samples according to optimized Freundlich adsorption coefficients. This was unexpected since it was assumed that the soil surface area available for sorption processes is greater or at least far more accessible if the unstructured fine earth is exposed to the phosphate solution. We conclude that if the inner pore space of soil aggregates is readily accessible and diffusion is not hindered, the overall retention capacity of intact aggregates might be higher than that of the disturbed soil because the intra-aggregate pore space can accommodate a certain fraction of phosphate in addition to the adsorbed amount at particle surfaces. The presented experimental approach allows for studying sorption processes in well-structured and fine earth in conditions that perform better compared to the natural situation. Additional testing of the method for different soil types is advisable.

Removal and biomineralization of Pb2+ in water by fungus Phanerochaete chrysoporium

The removal and biomineralization of Pb2+ (200 mg/L) in water were investigated utilizing mature mycelia of Phanerochaete chrysoporium. Mycelial dosage, initial Pb2+ concentration, solution pH and treatment time all were shown to have an influence on Pb2+ removal. Granular, lead-containing precipitation was formed on the fungal hyphae upon exposure to lead nitrate, which was confirmed from scanning electron micrograph/Energy Dispersive Spectrometer (SEM/EDS). Energy dispersive X-ray spectroscopic analysis revealed the presence of lead (48.5% by weight) along with phosphorus in the precipitate. This extracellular precipitate was further identified as pyromorphite lead hydroxyphosphate [Pb5(PO4)3OH] by X-ray powder diffraction (XRD) analysis. During Pb2+ removal, size-enlarged mineral precipitation, and clustered nanospherical particles formed on the hyphae were revealed by SEM/XRD. A remarkable increase of mycelial phosphatase activity of 1.5 times that of the control and decreased phosphate concentration in solution (16.76 mg/L to 1.39 mg/L) initially upon exposure to Pb2+ suggested that phosphatase may hydrolyze organic phosphorus into inorganic phosphate and release it into solution, participating in the biomineralization of Pb2+. Toxicity tests showed that the toxicity of Pb2+ polluted water decreased after treatment. The results clearly demonstrate previously unknown lead biomineralization as pyromorphite through fungal phosphatase.