The Identification and Synthesis of Lead Apatite Minerals Formed in Lead Water Pipes

Abstract

Phosphate is added to drinking water in the UK to minimise the release of lead from lead water pipes. The phosphate encourages the formation of insoluble lead apatites on the walls of the pipe. Hydroxylpyromorphite Pb5(PO4)3OH is the lead apatite that is most often used to model lead levels in tap water; however, its presence has not been confirmed. Our aims were to identify the lead pipe apatite and synthesise it. The synthetic mineral would then be used in future solubility studies to produce better predictions of lead levels in tap water. XRD and FTIR were used to characterise the minerals on a range of lead pipes. Pyromorphite and hydroxylpyromorphite were absent and instead a range of mixed calcium lead apatites were present. For every five lead ions in the general formula Pb5(PO4)3X between one and two ions were replaced with calcium and there was evidence of substitution ofPO43-by eitherCO32-orHPO42-. Calcium lead apatites with similar unit cell dimensions to those found on lead water pipes were then synthesised. The calcium : lead ratio in these reaction mixtures was in excess of 500 : 1 and the resulting crystals were shown by TEM to be nanosized rods and flakes. The synthetic apatites that most closely resembled the unit cell dimensions of the apatites on lead water pipes were shown to be Pb3.4Ca1.3(PO4)3Cl0.03OH0.97, Pb3.6Ca1.2(PO4)3Cl0.07OH0.93, and Pb3.6Ca1.2(PO4)3Cl0.27OH0.73.

Influence of phosphate dosing on biofilms development on lead in chlorinated drinking water bioreactors

“…Peters et al 34 , using spectrometric techniques to study lead service drinking water pipes, showed that lead carbonates were formed under pH adjusted-waters, and species like apatite were observed when orthophosphoric acid was added. This is in agreement with Hopwood et al 35 , who found that lead water pipes from Yorkshire (UK), fed with PO 4 3− treated drinking water, contained a variety of apatite minerals, included lead apatite species which are the least soluble form of lead 36 . In addition, microorganisms have the potential to induce metal precipitation in a range of environmental settings.…”

Water quality–pipe deposit relationships in Midwestern lead pipes

“…However, there are many uncertainties and potential errors in the simulations resulting from the absence or choice of equilibrium constants, variations in the physical solubility due to different solid phase purity and crystallinity, temperature-dependent variations of the equilibrium constants, and unknown rates of precipitation versus dissolution reactions (Edwards, Jacobs, & Dodrill, 1999;Noel, Wang, & Giammar, 2014;Schock & Sandvig, 2004). For example, studies have not conclusively determined the factors causing the specific formation of observed Pb(II) orthophosphate solids such as Pb 5 (PO 4 ) 3 OH (hydroxypyromorphite), Pb 5 (PO 4 ) 3 Cl (pyromorphite), or tertiary lead phosphates (Pb 3 (PO 4 ) 2 , Pb 9 (PO 4 ) 6 ) (Hopwood et al, 2016). Furthermore, studies Hayes, Croft, Phillips, Craik, & Schock, 2016;Kim & Herrera, 2010;Schock, Cantor, Triantafyllidou, Desantis, & Scheckel, 2014;Snoeyink et al, 2003;Wasserstrom, Miller, Triantafyllidou, Desantis, & Schock, 2017) have noted the extensive presence of amorphous solid phases in a number of drinking water distribution systems (DWDSs).…”

Trace Voltammetric Determination of Lead at a Recycled Battery Carbon Rod Electrode

“…The EU recognizes Pb as one of the substances known to cause direct health impacts, and as a result has proposed to lower the drinking water limit to 5 µg/L [5]. However, a number of reports from both the EU [6] and regions outside, such as the USA [7], Australia [8] and Pakistan, [9] have highlighted Pb drinking water levels that exceed this level.…”