Journal of Crystal Growth 237–239 (2002) 424–429 Investigation into the effect of phosphonate inhibitors on barium sulfate precipitation F. Jones, A. Oliveira, A.L. Rohl*, G.M. Parkinson, M.I. Ogden, M.M. Reyhani Department of Applied Chemistry, A.J. Parker Co-operative Research Centre for Hydrometallurgy, Curtin University of Technology, G.P.O. Box U1987, Perth, WA 6845, Australia Abstract The effect of a series of phosphonate molecules on barium sulfate precipitation was tested. While an increase in the number of phosphonate groups generally resulted in increased inhibition of barium sulfate precipitation, two notable exceptions showed that a relatively high number of phosphonate groups does not guarantee inhibition while a relatively low number of phosphonate groups does not imply no inhibition. Increasing the pH showed an increased effect of additives on barium sulfate precipitation up to pH 8. However, on increasing from pH 8 to 12, a loss of inhibition in the additives was observed which appears to be due to the barium sulfate surface changing with pH. r 2002 Elsevier Science B.V. All rights reserved. PACS: 80.10.Dn; 61.72.S Keywords: A1. Growth from solutions; A1. Impurities; B1. Barium compounds; B1. Organic compounds 1. Introduction Scale occurs in many processes ranging from desalination to oil production and results in costs associated with its removal. Barium sulfate is a known scale that is particularly prevalent in oil production [1,2]. The solid has a low solubility product [3], K sp B10 9:99 but solubility is found to increase when electrolytes are present. Since much literature exists on barium sulfate and since it is an industrial scale problem, barium sulfate appears to be a suitable choice as a model compound to investigate the factors which affect scale forma- tion. To this end, isostructural compounds were selected to ascertain the effects of chemical factors and shape factors on precipitation inhibition behavior. For this purpose, the effect of various phosphonate-based organics on the precipitation of barium sulfate was experimentally determined. These experimental results will be combined with molecular modelling studies in the future as part of a holistic approach to determine how scale inhibitors function. The following organics were investigated (Fig. 1): ethylenediaminetetraphosphonic acid (EDTP) hydroxyethylenediphosphonic acid (HEDP) N-methyl-nitrilodimethylene phosphonic acid (MNDP) nitrilodimethylenephosphonic acid (NDP) nitrilotrimethylenephosphonic acid (NTMP) and tetraazocyclododecanetetramethylenephospho- *Corresponding author. Tel.: +618-9266-7317; fax: +618- 9266-2300. E-mail address: andrew@power.curtin.edu.au (A.L. Rohl). 0022-0248/02/$-see front matter r 2002 Elsevier Science B.V. All rights reserved. PII:S0022-0248(01)01961-3