Optimized Procedure for Determining the Adsorption of Phosphonates onto Granular Ferric Hydroxide using a Miniaturized Phosphorus Determination Method

Abstract

This paper introduces a procedure to investigate the adsorption of phosphonates onto iron-containing filter materials, particularly granular ferric hydroxide (GFH), with little effort and high reliability. The phosphonate, e.g., nitrilotrimethylphosphonic acid (NTMP), is brought into contact with the GFH in a rotator in a solution buffered by an organic acid (e.g., acetic acid) or Good buffer (e.g., 2-(N-morpholino)ethanesulfonic acid) [MES] and N-cyclohexyl-2-hydroxyl-3-aminopropanesulfonic acid [CAPSO]) in a concentration of 10 mM for a specific time in 50 mL centrifuge tubes. Subsequently, after membrane filtration (0.45 µm pore size), the total phosphorus (total P) concentration is measured using a specifically developed determination method (ISOmini). This method is a modification and simplification of the ISO 6878 method: a 4 mL sample is mixed with H2SO4 and K2S2O8 in a screw cap vial, heated to 148-150 °C for 1 h and then mixed with NaOH, ascorbic acid and acidified molybdate with antimony(III) (final volume of 10 mL) to produce a blue complex. The color intensity, which is linearly proportional to the phosphorus concentration, is measured spectrophotometrically (880 nm). It is demonstrated that the buffer concentration used has no significant effect on the adsorption of phosphonate between pH 4 and 12. The buffers, therefore, do not compete with the phosphonate for adsorption sites. Furthermore, the relatively high concentration of the buffer requires a higher dosage concentration of oxidizing agent (K2S2O8) for digestion than that specified in ISO 6878, which, together with the NaOH dosage, is matched to each buffer. Despite the simplification, the ISOmini method does not lose any of its accuracy compared to the standardized method.

Batch Studies of Phosphonate and Phosphate Adsorption on Granular Ferric Hydroxide (GFH) with Membrane Concentrate and Its Synthetic Replicas

“…For phosphorus analysis, a modification of the ISO 6878 [25] method was used (ISO mini ). The ISO mini molybdenum blue method has been described in detail by Rott et al [22]. Prior to analysis, all glass materials that came into contact with the sample were thoroughly rinsed with 10% hydrochloric acid and deionized water.…”

“…Since synthetic wastewater lacks the buffering capacity of real wastewater, the addition of an organic buffer (0.01 M) was necessary to keep the pH stable during the adsorption experiments. The influence of the buffers on phosphorus analysis is negligible [22]. After the required amount of adsorbent was weighed into a 50 mL centrifuge tube, the tube was filled with the buffered P-containing solution up to the 50 mL mark, immediately capped, and then clamped in the overhead rotator (LLG-uniROTATOR 2) running at 20 rpm.…”

Behavior of PBTC, HEDP, and Aminophosphonates in the Process of Wastewater Treatment

“…The ISO specifically mentions that for some polyphosphonic acids up to 90 min of digestion are required. Furthermore, it was shown for all five phosphonates in Figure 1 that a total oxidation of organic P to phosphate-P is ensured with K 2 S 2 O 8 and H 2 SO 4 as proposed by ISO 6878 and applied in the cuvette rapid tests [20]. For the determination of dissolved P and o-PO 4 -P, the samples were filtered prior to digestion and analysis (cellulose-nitrate membrane filter with 0.45 µm pore width).…”