Effect Of PO4 Research Articles

Mechanistic Study of Pb(II) Removal by TiO2 and Effect of PO4.

As a commercial adsorbent, TiO2 shows a high adsorption capacity for lead (Pb(II)). However, the molecular structure of Pb(II) adsorption on TiO2 is still unknown. Meanwhile, as a widely used corrosion inhibitor, phosphate (PO4) is usually added into drinking water, and its influential mechanism on Pb(II) removal by TiO2 remains unknown. Here, the mechanisms of Pb(II) adsorption on TiO2 and the effect of PO4 were systematically investigated using a combination of spectroscopic analyses and surface complexation modeling. The adsorption structure of Pb(II) on TiO2 was revealed as a tridentate mononuclear configuration by the extended X-ray absorption fine structure (EXAFS) analysis. In the presence of 0.1-5 mg/L PO4, Pb(II) was removed mainly by adsorption on TiO2 rather than precipitation. Ternary complexation between Pb(II) and PO4 on TiO2 surfaces was found based on EXAFS and in situ Fourier transform infrared characterizations. These complexation structures were used to build a surface complexation model to accurately simulate and predict Pb(II) removal under different conditions. This study provides essential information about the mechanisms of Pb(II) removal by TiO2 and develops a model to predict adsorption behaviors, especially in the presence of PO4.

Growth dynamics of vaterite in relation to the physico-chemical properties of its precursor, amorphous calcium carbonate, in the Ca-CO3-PO4system

Vaterite is one of three non-hydrate calcium carbonate crystalline polymorphs and is formed as an initial phase under pseudo-biological conditions. However, biological hard tissues that use vaterite are rare; the reason for vaterite rarely appearing in vivo is still unclear. There is consensus that, in phosphate-containing solutions, vaterite barely forms and amorphous calcium carbonate (ACC), the precursor of crystalline calcium carbonate and considered as aggregation of growth unit of vaterite, is stabilized. In this study, to clarify the biomineralization process, we investigated how phosphate acts as an inhibitor of vaterite growth. We measured vaterite growth rates in situ and estimated the essential crystal growth parameter, edge free energy, in the Ca-CO3-PO4 system in relation to the physico-chemical properties of ACC. The effects of PO4 on the ACC structure and dynamics were also observed.

Survival, reproduction, and arsenic body burdens in Chironomus riparius exposed to arsenate and phosphate

Despite the increasing awareness of arsenic (As) contamination in surface waters worldwide, little is known about how As alone and in the presence of other chemicals affects aquatic insects. Larvae of Chironomus riparius were exposed in a laboratory investigation to factorial combinations of 0, 0.13, 2.0, 5.3, and 13μmolAsl−1 and 0, 0.15, and 15μmolPO4l−1 throughout development from first instar to pupal emergence. The time between male and female emergence increased from 1.8±0.17days to 2.9±0.34days with exposure at higher As levels. The highest As exposure also decreased the number of eggs per egg mass, which may affect population maintenance. For these parameters, there was no effect from PO4, and no interaction between As and PO4. Total As determination of larval and adult tissues was conducted using Hydride Generated Atomic Absorption Spectroscopy (HGAAS) and revealed concentrations ranging from 2.48±0.363 to 30.5±0.473μg/g and 1.03±0.286 to 8.97±0.662μg/g, respectively, indicating elimination of approximately 72% of total As body burdens between the fourth instar and adult stages. There was no effect of PO4, indicating PO4 does not alter uptake of As in C. riparius. The potential for movement of As to terrestrial systems exists, though trophic transfer may be more likely during the aquatic larval stage.

Greedy algae reduce arsenate

Algae reduce and methylate arsenate, producing arsenite (As(III)) when the growth rates are high and dimethylarsinic acid (DMA) when the growth rates are low. In lakes, this leads to high As(III) concentrations in the early stages of spring and fall blooms and high DMA concentrations in the summer. We hypothesize that under phosphorus (P)‐limited conditions, which usually exist in the summer, algae take up phosphate (PO4) and, because of similar chemical characteristics, As(V) as well. Inside the cell, As(V) is reduced to As(III), methylated to monomethylarsonic acid (MMA) and DMA, and then excreted. However, under non—P‐limited conditions, which exist in the early stages of blooms, algae up‐regulate their PO4 transport system to take up excess P, a phenomenon known as luxury uptake. Since As(V) is taken up by the PO4 transport system, As(V) uptake also increases at this time. Within the cell, the reduction of As(V) to As(III) is fast, but methylation is slower, causing As(III) to build up in the cell and be excreted, which, in turn, causes an increase in extracellular As(III). This mechanism permits the synergistic (luxury uptake) and antagonistic (competition) effects of PO4 on As(V) uptake and can therefore explain the seemingly contradictory results found in the literature. A mathematical model is constructed on the basis of existing established algal—nutrient interaction models and is used to simulate As transformation in two laboratory batch experiments. In addition to algal and P responses, the model can reasonably well reproduce the observed As(III) peak during the log growth phase and the more gradual appearance of DMA during the stationary phase.

The effect of the anions, phosphate and sulphate, on normal rates of excretion of potassium in dogs.

Small doses of (NH4)2HPO4 or KH2PO4 by stomach tube caused increase in plasma PO4 and PO4 excretion. Above a threshold of 0-8 mmol. 1(-1), increase of plasma PO4 by 0-5 mmol. 1(-1) caused PO4 excretion to increase by about 35 mumol. min.-1 After KH2PO4 this relationship was not altered by the concurrent increases in plasma K and K excretion. After doses of (NH4)2SO4 or K2SO4, excretion of SO4 was similarly related to plasma SO4 and was independent of plasma K and K excretion. An effect of PO4 on K excretion was observed after doses of (NH4)2HPO4, when increased excretion of PO4 was accompanied by increased excretion of K without change in plasma K. There was also increased excretion of NH4 and a small increase in Na excretion. The changes were similar to those produced by (NH4)2SO4 [O'Connor and Summerill, 1976]. KH2PO4 and K2SO4 produced increase in plasma K and increased excretion of K not significantly different from the changes produced by KCl or KHCO3 [Baylis and O'Connor, 1976]. After KH2PO2 or K2SO4, the urinary anion was PO4 or SO4, instead of Cl and HCO3. Any effect of anions on K excretion was much less than the effect of increase in plasma K. At low rates of excretion of K, increased urinary excretion of impermeant anion can determine increased excretion of K. However, the effect of anion is small in comparison with the effect of increase in plasma K.