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1. Preventing the colloidal dispersion of Pb( iv ) corrosion scales and lead release in drinking water distribution systems

   https://doi.org/10.1039/C9EW00231F  

   Korshin, Gregory ; Liu, Haizhou ( June 2019 , Environmental Science: Water Research & Technology)

   Lead( iv ) oxide PbO 2 is one dominant solid phase in lead corrosion scales of drinking water distribution systems. Understanding the colloidal dispersion of PbO 2 is important for lead control in drinking water, especially under scenarios of switching the residual disinfectant from chlorine to chloramine. This study investigated the changes in lead release and colloidal dispersion from PbO 2(s) associated with the presence of natural organic matter (NOM), the introduction of chloramine, and the addition of a phosphate corrosion inhibitor in drinking water distribution systems. Experimental data showed that when NOM was present, the surface charges of PbO 2 exhibited a prominent negative shift, leading to colloidal dispersion of Pb( iv ) particles. The presence of chloramine did not significantly change the detrimental effects of NOM on the colloidal behavior of PbO 2 . In contrast, the addition of phosphate greatly reduced colloidal lead release in the size range between 0.1 and 0.45 μm, and limited lead release with colloidal sizes less than 0.1 μm to below 15 μg L −1 , i.e. , the U.S. EPA regulatory standard. The beneficial effects of phosphate addition are mainly attributed to the suppression in colloidal dispersion of Pb( iv )more »particles. Meanwhile, the presence of phosphate also limits the reductive dissolution of PbO 2 via the formation of hydroxypyromorphite Pb 5 (PO 4 ) 3 OH particles. Results from this study suggest that phosphate limits the dispersion of PbO 2(s) by NOM and prevented the release of Pb( iv ) colloids into drinking water.« less
2. Emerging investigators series: comparing the inherent reactivity of often-overlooked aqueous chlorinating and brominating agents toward salicylic acid

   https://doi.org/10.1039/C7EW00491E  

   Broadwater, Matthew A. ; Swanson, Tyler L. ; Sivey, John D. ( January 2018 , Environmental Science: Water Research & Technology)

   Chlorinated and brominated forms of salicylic acid (SA) have recently been identified as a new class of disinfection byproducts (DBPs) in drinking water. Herein, we report the inherent reactivity of several aqueous halogenating agents toward hydrogen salicylate, the predominant species of salicylic acid under environmental conditions. Using synthetic waters, halogenation rates associated with the formation of 3-chloro, 5-chloro, 3-bromo, and 5-bromosalicylate were measured as a function of pH, [Cl − ], [Br − ], free chlorine dose, and the initial concentration of SA. Halogenating-agent specific second-order rate constants were determined and decrease in the order: BrCl > BrOCl > Br 2 > Br 2 O > Cl 2 > Cl 2 O > HOBr > HOCl. Chloride is capable of enhancing rates of bromination and chlorination, ostensibly by promoting the formation of BrCl and Cl 2 , both of which are several orders of magnitude more inherently reactive than HOBr and HOCl, respectively. Kinetic data also support the participation of salicyloyl hypochlorite as a chlorination intermediate capable of influencing chlorination rates at pH >8. Experiments in which buffer concentrations were varied indicate that phosphate buffers can enhance rates of SA bromination but not chlorination; carbonate and borate buffers did notmore »appreciably influence rates of bromination or chlorination. Under conditions representative of chlorinated drinking water, rates of SA bromination will generally exceed rates of SA chlorination. The results discussed herein demonstrate the importance of considering halogenating agents beyond HOBr and HOCl when developing kinetic models to describe and predict halogenation rates and selectivity in waters containing free chlorine.« less
3. Pb Mineral Precipitation in Solutions of Sulfate, Carbonate and Phosphate: Measured and Modeled Pb Solubility and Pb2+ Activity

   https://doi.org/10.3390/min11060620  

   Li, Xinxin ; Azimzadeh, Behrooz ; Martinez, Carmen Enid ; McBride, Murray B. ( June 2021 , Minerals)

   Lead (Pb) solubility is commonly limited by dissolution–precipitation reactions of secondary mineral phases in contaminated soils and water. In the research described here, Pb solubility and free Pb2+ ion activities were measured following the precipitation of Pb minerals from aqueous solutions containing sulfate or carbonate in a 1:5 mole ratio in the absence and presence of phosphate over the pH range 4.0–9.0. Using X-ray diffraction and Fourier-transform infrared spectroscopic analysis, we identified anglesite formed in sulfate-containing solutions at low pH. At higher pH, Pb carbonate and carbonate-sulfate minerals, hydrocerussite and leadhillite, were formed in preference to anglesite. Precipitates formed in the Pb-carbonate systems over the pH range of 6 to 9 were composed of cerussite and hydrocerussite, with the latter favored only at the highest pH investigated. The addition of phosphate into the Pb-sulfate and Pb-carbonate systems resulted in the precipitation of Pb3(PO4)2 and structurally related pyromorphite minerals and prevented Pb sulfate and carbonate mineral formation. Phosphate increased the efficiency of Pb removal from solution and decreased free Pb2+ ion activity, causing over 99.9% of Pb to be precipitated. Free Pb2+ ion activities measured using the ion-selective electrode revealed lower values than predicted from thermodynamic constants, indicating that the precipitatedmore »minerals may have lower KSP values than generally reported in thermodynamic databases. Conversely, dissolved Pb was frequently greater than predicted based on a speciation model using accepted thermodynamic constants for Pb ion-pair formation in solution. The tendency of the thermodynamic models to underestimate Pb solubility while overestimating free Pb2+ activity in these systems, at least in the higher pH range, indicates that soluble Pb ion-pair formation constants and KSP values need correction in the models.« less
4. Bromide-assisted catalytic oxidation of lead( ii ) solids by chlorine in drinking water distribution systems

   https://doi.org/10.1039/C7CC02533E  

   Orta, John ; Patton, Samuel ; Liu, Haizhou ( January 2017 , Chemical Communications)

   This study investigated the effect of bromide on the oxidation of three lead( ii ) solids by chlorine – a redox process critical to the control of lead release in drinking water distribution systems. Bromide had a strong catalytic effect on the oxidation of lead( ii ) carbonate solids, but had a limited impact on the oxidation of lead( ii ) phosphate.
5. Applications of 1,3,5-trimethoxybenzene as a derivatizing agent for quantifying free chlorine, free bromine, bromamines, and bromide in aqueous systems

   https://doi.org/10.1039/C9AY01443H  

   Dias, Ryan P. ; Schammel, Marella H. ; Reber, Keith P. ; Sivey, John D. ( January 2019 , Analytical Methods)

   Free chlorine and free bromine ( e.g. , HOCl and HOBr) are employed as disinfectants in a variety of aqueous systems, including drinking water, wastewater, ballast water, recreational waters, and cleaning products. Yet, the most widely used methods for quantifying free halogens, including those employing N , N -diethyl- p -phenylenediamine (DPD), cannot distinguish between HOCl and HOBr. Herein, we report methods for selectively quantifying free halogens in a variety of aqueous systems using 1,3,5-trimethoxybenzene (TMB). At near-neutral pH, TMB reacted on the order of seconds with HOCl, HOBr, and inorganic bromamines to yield halogenated products that were readily quantified by liquid chromatography or, following liquid–liquid extraction, gas chromatography-mass spectrometry (GC-MS). The chlorinated and brominated products of TMB were stable, and their molar concentrations were used to calculate the original concentrations of HOCl (method quantitation limit (MQL) by GC-MS = 15 nmol L −1 = 1.1 μg L −1 as Cl 2 ) and HOBr (MQL by GC-MS = 30 nmol L −1 = 2 μg L −1 as Cl 2 ), respectively. Moreover, TMB derivatization was efficacious for quantifying active halogenating agents in drinking water, pool water, chlorinated surface waters, and simulated spa waters treated with 1-bromo-3-chloro-5,5-dimethylhydantoin. TMB wasmore »also used to quantify bromide as a trace impurity in 20 nominally bromide-free reagents (following oxidation of bromide by HOCl to HOBr). Several possible interferents were tested, and iodide was identified as impeding accurate quantitation of HOCl and HOBr. Overall, compared to the DPD method, TMB can provide lower MQLs, larger linear ranges, and selectivity between HOCl and HOBr.« less