Dissolution and solubility of the arsenate - phosphate hydroxylapatite solid solution [Ca5(PxAs1 - xO4)3(OH)] at 25°C

Abstract

Environmental context. Apatites form a large family of minerals and compounds that can incorporate a variety of ions, including arsenate that can substitute for phosphate. Apatites may therefore control the concentration of arsenic in some aqueous environments. This manuscript describes the synthesis and characterisation of the arsenate-phosphate hydroxylapatite solid solution and the solid solution-aqueous solution interaction.Abstract. Nine different members of the arsenate-phosphate hydroxylapatite solid solution [Ca 5 (P x As 1Àx O 4 ) 3 (OH)] were prepared and characterised by various techniques, and then dissolution of the synthetic solids was studied at 258C and pH 2 in a series of batch experiments. The concentrations of aqueous arsenate species increased rapidly at the beginning of the dissolution and reached a steady-state after 480 h. The concentrations of aqueous phosphate species increased very fast initially and reached a peak value within the first hour of dissolution and then declined slowly with time and remained constant after 240-360 h. The solubility of the Ca 5 (P x As 1Àx O 4 ) 3 (OH) solid solution increased and its stability decreased with an increase in the mole fraction of Ca 5 (AsO 4 ) 3 (OH). The dissolution followed or slightly overshot the Lippmann solutus curve, then approached the solutus curve. The Ca 5 (AsO 4 ) 3 (OH)-poor solid solution was in equilibrium with the arsenate-rich aqueous solution.

Textural and compositional complexities resulting from coupled dissolution–reprecipitation reactions in geomaterials

“…It is also influenced by the relative solubilities of the end members, with similar end member solubilities defining a larger range of intermediate compositions ( Fig. 13; Prieto et al 1997;Zhang et al 2011). (Fig.…”

“…The reaction path was developed based on the starting conditions of Putnis and Mezger (2004), with S 0 and S f representing initial and final solid compositions. b) Ideal Lippmann diagram for the hydroxylapatite-johnbaumite-H 2 O SSAS system developed using solubility products of Zhang et al (2011). The reaction path follows that described by Borg et al (2014).…”

Complex mineral zoning patterns caused by ultra-local equilibrium at reaction interfaces

“…This reaction is also controlled by relative solubility. Arsenic-rich hydroxylapatite is more soluble than As-poor hydroxylapatite (e.g., Zhang et al, 2011) so treatment of As-bearing apatite with more phosphate-rich solutions leads to complete homogenization of the As (Fig. 1D).…”

Microanalytical study of copper ores from the Chalcolithic settlement of São Pedro (Portugal): Copper production in the south‐western Iberian Peninsula

“…; Zhang et al . ). These aspects can explain part of the results obtained, especially the combined association of As with Cu and phosphorous, which would suggest its incorporation in the libethenite structure as observed in sample SP1635.…”