Acid-rock reaction kinetics in a two-scale model based on reaction order correction

The reaction order plays a crucial role in evaluating the response rate of acid-rock.However,the conventional two-scale model typically assumes that the reaction order is constant as one,which can lead to significant deviations from reality.To address this issue,this study proposes a novel multi-order dynamic model for acid-rock reaction by combining rotating disk experimental data with theoretical derivation.Through numerical simulations,this model allows for the investigation of the impact of acidification conditions on different orders of reaction,thereby providing valuable insights for on-site construction.The analysis reveals that higher response orders require higher optimal acid liquid flow rates,and lower optimal H+diffusion coefficients,and demonstrate no significant correlation with acid concentration.Consequently,it is recommended to increase the displacement and use high-viscosity acid for reservoirs with high calcite content,while reducing the displacement and using low-viscosity acid for reservoirs with high dolomite content.

Tuning electronic structure of RuO_(2)by single atom Zn and oxygen vacancies to boost oxygen evolution reaction in acidic medium

The poor stability of RuO_(2)electrocatalysts has been the primary obstacles for their practical application in polymer electrolyte membrane electrolyzers.To dramatically enhance the durability of RuO_(2)to construct activity-stability trade-off model is full of significance but challenging.Herein,a single atom Zn stabilized RuO_(2)with enriched oxygen vacancies(SA Zn-RuO_(2))is developed as a promising alternative to iridium oxide for acidic oxygen evolution reaction(OER).Compared with commercial RuO_(2),the enhanced Ru–O bond strength of SA Zn-RuO_(2)by forming Zn-O-Ru local structure motif is favorable to stabilize surface Ru,while the electrons transferred from Zn single atoms to adjacent Ru atoms protects the Ru active sites from overoxidation.Simultaneously,the optimized surrounding electronic structure of Ru sites in SA ZnRuO_(2)decreases the adsorption energies of OER intermediates to reduce the reaction barrier.As a result,the representative SA Zn-RuO_(2)exhibits a low overpotential of 210 mV to achieve 10 mA cm^(-2)and a greatly enhanced durability than commercial RuO_(2).This work provides a promising dual-engineering strategy by coupling single atom doping and vacancy for the tradeoff of high activity and catalytic stability toward acidic OER.

A cleaner production strategy for acid mine drainage prevention of waste rock:A porphyry copper case

An in-process technology approach is proposed to identify the source of acid mine drainage(AMD)generation and prevent its formation in a porphyry copper waste rock(WR).Adopting actions before stockpiling the WR enables the establishment of potential contaminants and predicts the more convenient method for AMD prevention.A WR sample was separated into size fractions,and the WR’s net acidgenerating potential was quantified using chemical and mineralogical characterization.The diameter of physical locking of sulfides(DPLS)was determined,and the fractions below the DPLS were desulfurized using flotation.Finally,the WR fractions and tailing from the flotation test were submitted to acid-base accounting and weathering tests to evaluate their acid-generating potential.Results show that the WR’s main sulfide mineral is pyrite,and the DPLS was defined as 850μm.A sulfide recovery of 91%was achieved using a combination of HydroFloat^(®)and Denver cells for a size fraction lower than DPLS.No grinding was conducted.The results show that size fractions greater than DPLS and the desulfurized WR are unlikely to produce AMD.The outcomes show that in-processing technology can be a more proactive approach and an effective tool for avoiding AMD in a porphyry copper WR.

Boric Acid-Assisted Pyrolysis for High-Loading Single-Atom Catalysts to Boost Oxygen Reduction Reaction in Zn-Air Batteries

The emerging of single-atom catalysts(SACs)offers a great opportunity for the development of advanced energy storage and conversion devices due to their excellent activity and durability,but the actual mass production of high-loading SACs is still challenging.Herein,a facile and green boron acid(H_(3)BO_(3))-assisted pyrolysis strategy is put forward to synthesize SACs by only using chitosan,cobalt salt and H_(3)BO_(3)as precursor,and the effect of H_(3)BO_(3)is deeply investigated.The results show that molten boron oxide derived from H_(3)BO_(3)as ideal high-temperature carbonization media and blocking media play important role in the synthesis process.As a result,the acquired Co/N/B tri-doped porous carbon framework(Co-N-B-C)not only presents hierarchical porous structure,large specific surface area and abundant carbon edges but also possesses high-loading single Co atom(4.2 wt.%),thus giving rise to outstanding oxygen catalytic performance.When employed as a catalyst for air cathode in Zn-air batteries,the resultant Co-N-B-C catalyst shows remarkable power density and long-term stability.Clearly,our work gains deep insight into the role of H_(3)BO_(3)and provides a new avenue to synthesis of high-performance SACs.

Steam reforming of acetic acid over Ni/biochar of low metal-loading:Involvement of biochar in tailoring reaction intermediates renders superior catalytic performance

Biochar is a reactive carrier as it may be partially gasified with steam in steam reforming,which could influence the formation of reaction intermediates and modify catalytic behaviors.Herein,the Ni/biochar as well as two comparative catalysts,Ni/Al_(2)O_(3) and Ni/SiO_(2),with low nickel loading(2%(mass))was conducted to probe involvement of the varied carriers in the steam reforming.The results indicated that the Ni/biochar performed excellent catalytic activity than Ni/SiO_(2) and Ni/Al_(2)O_(3),as the biochar carrier facilitated quick conversion of the -OH from dissociation of steam to gasify the oxygen-rich carbonaceous intermediates like C=O and C-O-C,resulting in low coverage while high exposure of nickel species for maintaining the superior catalytic performance.In converse,strong adsorption of aliphatic intermediates over Ni/Al_(2)O_(3) and Ni/SiO_(2) induced serious coking with polymeric coke as the main type(21.5%and 32.1%,respectively),which was significantly higher than that over Ni/biochar(3.9%).The coke over Ni/biochar was mainly aromatic or catalytic type with nanotube morphology and high crystallinity.The high resistivity of Ni/biochar towards coking was due to the balance between formation of coke and gasification of coke and partially biochar with steam,which created developed mesopores in spent Ni/biochar while the coke blocked pores in Ni/Al_(2)O_(3) and Ni/SiO_(2) catalysts.

Insights into kinetics and reaction mechanism of acid-catalyzed transesterification synthesis of diethyl oxalate

The catalytic performance of different acidic catalysts for diethyl oxalate synthesis from the one-step transesterification of dimethyl oxalate and ethanol was evaluated.The effects of different factors(e.g.,acidity,electron accepting capacity,cations type and crystalline water)on the catalytic activity of acidic catalysts were investigated respectively.It was proposed and confirmed that the transesterification reaction catalyzed by a Lewis acid(FeCl3)and a Bronsted acid(H2SO4)follows a first-order kinetic reaction process.In addition,the Lewis acid-catalyzed transesterification processes with different ester structures were used to further explore and understand the speculated reaction mechanism.This work enriches the theoretical understanding of acid-catalyzed transesterification reactions and is of great significance for the development of highly active catalysts for diethyl oxalate synthesis,diminishing the industrial production cost of diethyl oxalate,and developing downstream bulk or high-value-added industrial products.

Progress on the mechanisms of Ru-based electrocatalysts for the oxygen evolution reaction in acidic media

Water electrolysis using proton-exchange membranes is one of the most promising technologies for carbon-neutral and sustainable energy production.Generally,the overall efficiency of water splitting is limited by the oxygen evolution reaction(OER).Nevertheless,a trade-off between activity and stability exists for most electrocatalytic materials in strong acids and oxidizing media,and the development of efficient and stable catalytic materials has been an important focus of research.In this view,gaining in-depth insights into the OER system,particularly the interactions between reaction intermediates and active sites,is significantly important.To this end,this review introduces the fundamentals of the OER over Ru-based materials,including the conventional adsorbate evolution mechanism,lattice oxygen oxidation mechanism,and oxide path mechanism.Moreover,the up-to-date progress of representative modifications for improving OER performance is further discussed with reference to specific mechanisms,such as tuning of geometric,electronic structures,incorporation of proton acceptors,and optimization of metal-oxygen covalency.Finally,some valuable insights into the challenges and opportunities for OER electrocatalysts are provided with the aim to promote the development of next-generation catalysts with high activity and excellent stability.

Recent progress of advanced manganese oxide-based materials for acidic oxygen evolution reaction: Fundamentals, performance optimization,and prospects

The oxygen evolution reaction(OER) is the basis of various sustainable energy conversion and storage techniques,especially hydrogen production by water electrolysis.To realize the practical application of hydrogen energy and mass-scale hydrogen production via water electrolysis,several obstacles,such as the multi-electron transfer OER process with sluggish kinetics and overall high reaction barrier,should be overcome.Manganese oxide-based(MnOx) materials,especially MnO_(2),have emerged as promising non-noble electrocatalysts for water electro-oxidation under acidic conditions due to their wellbalanced properties between catalytic activity and stability.This review introduces the fundamental understanding of the catalytic OER process on MnOx-based materials,including the conventional adsorbate evolution mechanism(AEM) and emerging lattice oxygen oxidation mechanism(LOM).The rational screening and prediction of MnOx-based catalysts that can stably catalyze OER in acid are summarized based on Pourbaix diagram analysis and thermodynamic density functional theory(DFT) calculations.Then,the up-to-date progress of upgrading the OER catalytic performance of MnOx-based catalysts by composite construction is reviewed.Afterward,feasible strategies to improve the electrocatalytic activity and lifetime of MnOx-based catalysts are systemically discussed in terms of crystal structure control,reasonable setting of working potential and electrolyte environment,optimal selection of acid-stable conductive supports,and self-healing engineering.Finally,future scientific challenges and research directions are outlined to guide the construction of advanced MnOx-based electrocatalysts for OER in acid.

Exploration of optimal reaction conditions on lactic acid production from glucose photoreforming over carbon nitride

Biomass valorization by photoreforming approach provides a promising and alternative strategy to generate value-added chemicals and fuels.In this work,we demonstrate the selective production of lactic acid from glu-cose photoreforming over pristine graphitic carbon nitride(g-C_(3) N_(4))photocatalyst.Control experiments screen the best condition for the highest yield of lactic acid,including modulating pH,catalyst loading,and reaction time.100%glucose conversion is achieved along with almost 100%lactic acid yield under the optimized con-dition.Density functional theory(DFT)calculations reveal that the rate-determining step(RDS)of the overall reaction on g-C_(3) N_(4) is the conversion of pyruvaldehyde,where an electron transfer takes place.This present work provides experimental insights and theoretical understanding for selective lactic acid production from biomass photoreforming.

Pt-Te alloy nanowires towards formic acid electrooxidation reaction

The high-performance anodic electrocatalysts is pivotal for realizing the commercial application of the direct formic acid fuel cells.In this work,a simple polyethyleneimine-assisted galvanic replacement reaction is applied to synthesize the high-quality PtTe alloy nanowires(PtTe NW)by using Te NW as an efficient sacrificial template.The existence of Te atoms separates the continuous Pt atoms,triggering a direct reaction pathway of formic acid electrooxidation reaction(FAEOR)at PtTe NW.The one-dimensional architecture and highly active sites have enabled PtTe NW to reveal outstanding electrocatalytic activity towards FAEOR with the mass/specific activities of 1091.25 mA mg^(-1)/45.34 A m^(-2)at 0.643 V potential,which are 44.72/23.16 and 20.26/11.75 times bigger than those of the commercial Pt and Pd nanoparticles,respectively.Density functional theory calculations reveal that Te atoms optimize the electronic structure of Pt atoms,which decreases the adsorption capacity of CO intermediate and simultaneously improves the durability of PtTe NW towards FAEOR.This work provides the valuable insights into the synthesis and design of efficient Pt-based alloy FAEOR electrocatalysts.

Deoxyribonucleic Acid-Polymerase Chain Reaction Status of HIV Exposed Infants in a Sub Regional Prevention of Mother-to-Child Transmission of HIV Programme during the Period 2009-2020

Introduction: Transitioning to more efficacious Antiretrovirals for HIV infected pregnant women and infant prophylaxis has reduced Mother to child transmission of HIV significantly. This study aimed to determine HIV infection status in HIVexposed infants who had their first DNA polymerase chain reaction test in our molecular Laboratory. Subjects, Materials and Methods: Dried Blood Spots for HIV DNA results from 5 states between 2009 and 2020 were analyzed in the PCR laboratory of the Federal Teaching Hospital, Gombe. Results: Nine thousand eight hundred and twenty-three Human Immunodeficiency Virus Deoxyribonucleic acid polymerase Chain Reaction results were analysed;4937 (50.2%) were males. During the study period, there was an overall declining trend in the mother-to-child transmission rate from 3.8% in 2009 to 1.0% in 2020. 6120 (62.3%) of HIV + mothers received Highly active antiretroviral therapy HAART before pregnancy. 7845 (76.2%) of the infants received Nevirapine prophylaxis. Dried blood spot samples were collected from 4077 (41.5%) at 6 - 8 weeks. 8438 (85.9%) received cotrimoxazole. 9469 (96.4%) were ever breastfed. Of the 9823 HIV DNA PCR results, 255 (2.6%) were positive while 69/4077 (1.7%) and 109/2662 (4.1%) were positive for HIV DNA at 6 - 8 weeks and > 12 weeks respectively. (p = 0.001). 86/747 (11.5%) of infants whose HIV-positive mothers received no ARVS were HIV DNA positive. (p = 0.001). 106/884 (12.0%) of infants who had no Antiretroviral prophylaxis had positive HIV DNA results;7/413 (1.7%) with Zidovudine/Nevirapine prophylaxis had positive results. (p = 0.001). 246/9469 (2.6%) of infants that were ever breastfed were positive for HIV DNA;11/354 (3.0%) that never breastfed had positive HIV DNA. Conclusion: Lack of maternal/infant ARVs and prolonged breastfeeding increased the risk of infant HIV infection.

Ionic liquid-assisted preparation of hydroxyapatite and its catalytic performance for decarboxylation of itaconic acid

The synthesis of methacrylic acid from biomass-derived itaconic acid is a green route,for it can get rid of the dependence on fossil resource.In order to solve the problems on this route such as use of a preciousmetal catalyst and a corrosive homogeneous alkali,we prepared a series of hydroxyapatite catalysts by an ionic liquid-assisted hydrothermal method and evaluated their catalytic performance.The results showed that the ionic liquid[Bmim]BF_(4) can affect the crystal growth of hydroxyapatite,provide fluoride ion for fluorination of hydroxyapatite,and adjust the surface acidity and basicity,morphology,textural properties,crystallinity,and composition of hydroxyapatite.The[Bmim]BF4 dosage and hydrothermal temperature can affect the fluoride ion concentration in the hydrothermal system,thus changing the degree of fluoridation of hydroxyapatite.High fluoride-ion concentration can lead to the formation of CaF_(2) and thus significantly decrease the catalytic performance of hydroxyapatite.The hydrothermal time mainly affects the growth of hydroxyapatite crystals on the c axis,leading to different catalytic performance.The suitable conditions for the preparation of this fluoridized hydroxyapatite are as follows:a mass ratio of[Bmim]BF4 to calcium salt=0.2:1,a hydrothermal time of 12 h,and a hydrothermal temperature of 130℃.A maximal methacrylic acid yield of 54.7%was obtained using the fluoridized hydroxyapatite under relatively mild reaction conditions(250℃ and 2 MPa of N_(2))in the absence of a precious-metal catalyst and a corrosive homogeneous alkali.

Biomass-based production of trimellitic and trimesic acids

The production of industrial chemicals with renewable biomass feedstock holds potential to aid the world in pursuing a carbon-neutral society.Trimellitic and trimesic acids are important commodity chemicals in industry that are prepared by the oxidation of petroleum-derived trimethylbenzene.To reduce the dependence on the limited oil source,we develop a potential sustainable alternative towards trimellitic and trimesic acids using biomass-based 2-methyl-2,4-pentandiol(MPD),acrylate and crotonaldehyde as starting materials.The process for trimellitic acid includes dehydration/D-A reaction of MPD and acrylate,flow aromatization over Pd/C catalyst,hydrolysis and catalytic aerobic oxidation(60%overall yield).The challenging regioselectivity issue of D-A reaction is tackled by a matched combination of temperature and deep eutectic solvent ChCl/HCO_(2)H.Crotonaldehyde can also participate in the reaction,followed by Pd/C-catalyzed decarbonylation/dehydrogenation and oxidation to provide trimesic acid in 54%overall yield.Life cycle assessment implies that compared to conventional fossil process,our biomass-based routes present a potential in reducing carbon emissions.

Water-induced physicochemical and pore changes in limestone for surrounding rock across pressure aquifers

Osmotic water alters the physicochemical properties and internal structures of limestone.This issue is particularly critical in tunnel construction across mountainous regions with aquifers,where pressurized groundwater can destabilize the limestone-based surrounding rock.Thus,systematic research into the physicochemical properties and pore structure changes in the limestone under pressurized water is essential.Additionally,it is essential to develop an interpretable mathematical model to accurately depict how pressurized osmotic water weakens limestone.In this research,a specialized device was designed to simulate the process of osmotic laminar flow within limestone.Then,four main tests were conducted:mass loss,acoustic emission(AE),mercury intrusion porosimetry(MIP),and fluorescence analysis.Experimental results gained from tests led to the development of a“Particle-pore throat-water film”model.Proposed model explains water-induced physicochemical and pore changes in limestone under osmotic pressure and reveals evolutionary mechanisms as pressure increases.Based on experimental results and model,we found that osmotic pressure not only alters limestone composition but also affects pore throats larger than 0.1μm.Furthermore,osmotic pressure expands pore throats,enhancing pore structure uniformity,interconnectivity,and permeability.These effects are observed at a threshold of 7.5 MPa,where cohesive forces within the mineral lattice are surpassed,leading to the breakdown of erosion-resistant layer and a significant increase in hydrochemical erosion.

Syntheses,crystal structures,and catalytic properties of three zinc(Ⅱ),cobalt(Ⅱ)and nickel(Ⅱ)coordination polymers constructed from 5⁃(4⁃carboxyphenoxy)nicotinic acid

Three zinc(Ⅱ),cobalt(Ⅱ),and nickel(Ⅱ)coordination polymers,namely[Zn(μ^(3-)cpna)(μ-dpea)_(0.5)]_(n)(1),[Co(μ^(3-)cpna)(μ-dpey)_(0.5)]_(n)(2),and[Ni(μ^(3-)cpna)(μ-dpey)_(0.5)(H_(2)O)]_(n)(3),have been constructed hydrothermally using H_(2)cpna(5-(4-carboxyphenoxy)nicotinic acid),dpea(1,2-di(4-pyridyl)ethane),dpey(1,2-di(4-pyridyl)ethylene),and zinc,cobalt,and nickel chlorides at 160℃.The products were isolated as stable crystalline solids and were characterized by IR spectra,elemental analyses,thermogravimetric analyses,and single-crystal X-ray diffraction analyses.Single-crystal X-ray diffraction analyses revealed that three compounds crystallize in the triclinic system,space group P1.Compounds 1-3 show 2D layer structures.The catalytic activities in the Knoevenagel condensation reaction of these compounds were investigated.Compounds 1 and 2 exhibit effective catalytic activities in the Knoevenagel condensa-tion reaction at room temperature.For this reaction,various parameters were optimized,followed by the investiga-tion of the substrate scope.CCDC:2335676,1;2335677,2;2335678,3.

RuO_(2)/CoMO_(2)O_(x) Catalyst with Low Ruthenium Loading for Long-Term Acidic Oxygen Evolution

We must urgently synthesize highly efficient and stable oxygen-evolution reaction(OER) catalysts for acidic media. Herein, we constructed a series of Ti mesh(TM)-supported RuO_(2)/CoMo_(y)O_(x) catalysts(RuO_(2)/CoMo_(y)O_(x)/TM) with heterogeneous structures. By optimizing the ratio of Co to Mo, RuO_(2)/CoMO_(2)O_(x)/TM with low Ru loading(0.079 mg/cm^(2)) achieves remarkable OER performance(η = 243 mV at 10 mA/cm^(2)) and high stability(300 h @ 10 mA/cm^(2)) in 0.5 mol/L H_(2)SO_(4) electrolyte. The activity of RuO_(2)/CoMo_yO_x/TM can be maintained for 50 h at 100 mA/cm^(2), and a water electrolyzer with RuO_(2)/CoMO_(2)O_(x)/TM as anode can operate for 40 h at 100 mA/cm~2, suggesting the remarkable OER durability of RuO_(2)/CoMo__(y)O__(x)/TM in acidic electrolyte. Owing to the heterogeneous interface between CoMO_(2)O_(x) and RuO_(2), the electronic structure of Ru atoms was optimized and electron-rich Ru was formed. With modulated electronic properties, the dissociation energy of H_(2)O is weakened, and the OER barrier is lowered. This study provides the design of low-cost noble metal catalysts with long-term stability in an acidic environment.

Electrolyte dependence for the electrochemical decarboxylation of medium-chain fatty acids (n-octanoic acid) into fuel on Pt electrode

The deoxygenation of organic acids, important biomass feedstocks and derivatives, to synthesize hydrocarbon products under mild electrochemical conditions, holds significant importance for the production of carbon-neutral biofuels. There is still limited research on the influential factors of the electrochemical decarboxylation reaction of medium-chain fatty acids. In this study, n-octanoic acid (OA) was chosen as the research subject to investigate the electrochemical decarboxylation behavior of OA on a platinum electrode, focusing on the influence of different alkali metal cations (Li^(+), Na^(+), K^(+)), common anions (SO^(4)^(2−), Cl^(−)), and electrolyte pH. It was found that KOH as an electrolyte exhibited the best performance for OA. Possibly, the larger size of K^(+) increased the alkalinity of the electrode surface, facilitating OA deprotonation. LiOH electrolyte reduced the solubility of OA, thereby inhibiting the decarboxylation reaction. SO^(4)^(2−) exhibited a weak promoting effect on the decarboxylation reaction of OA, while Cl^(−) showed no adverse effect although Cl^(−) may adsorb on the electrode surface. Furthermore, unlike short-chain fatty acids, medium-chain OA can only achieve efficient decarboxylation under alkaline conditions due to its solubility properties. This study provides references and foundations for future efforts to enhance the efficiency of electrochemical decarboxylation synthesis of hydrocarbon biofuels from medium-chain fatty acids.

Effects of Oleanolic Acid on the Immune Complex Allergic Reaction and Inflammation

When oleanolic acid (OA) was administered ig before and after sensitization on d 1 to d 5 and d 11 to d 17,it had no apparent effect on Arthus reaction.When it was administered at 48,24 and 1 h before challenge,however,Arthus reaction was significantly inhibited.OA showed markedly suppressive effects on reversible passive Arthus reaction and leukocyte migratory response.It could significantly stabilize erythrocyte membrane,inhibit the swelling of the rat's hind paw induced by in- jecting mycostatin,reduce the acid phosphatase content in the inflammatory exudate,suppress the syn- thesis or release of PGE,histamine,LTB4 and kinin,and the phlogistic action of PGE_2,histamine,5- HT and kinin.In addition,it could decrease the content of malonyldialdehyde (MDA) in hepatic tissue of alcohol-intoxicated mice,and increase the activity of catalase (CAT) in hepatic tissue of mice.OA had no apparent effect on the activity of super-oxide dismutase (SOD) in rat serum,on the content of immune complex in serum of rat with Arthus reaction,on the phagocytosis of monocytc-macrophage system,on the clearance of enzyme-containing immune complex by macrophage,or on the activity of total complement.

Hydrothermal synthesis of titanium-supported nanoporous palladium-copper electrocatalysts for formic acid oxidation and oxygen reduction reaction

Nanoporous Pd and binary Pd-Cu particles were prepared by a hydrothermal method using ethylene glycol as a reduction agent and they were directly immobilized on Ti substrates named as Ti-supported Pd-based catalysts. Their electrocatalytic activity for formic acid oxidation and oxygen reduction reaction （ORR） in alkaline media was examined by voltammetric techniques. Among the as-prepared catalysts, nanoPdslCu19/Ti catalyst presents the highest current density of 39.8 mA/cm2 at -0.5 V or 66.4 mA/cm2 at -0.3 V for formic acid oxidation. The onset potential of ORR on the nanoPdslCU19/Ti catalyst presents an about 70 mV positive shift compared to that on the nanoPd/Ti, and the current density of ORR at -0.3 V is 2.12 mA/cm2, which is 3.7 times larger than that on the nanoPd/Ti.

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.