Boron removal from oilfield produced water through a precipitation process with bottom ash leachate and Ca(OH)2

In this paper an innovative precipitation process that uses the leachate from the acid washing of combustion bottom ash (bottom ash leachate, BAL) together with Ca(OH)2 was developed for the removal of boron from water. Several batch experiments were conducted to identify the most suitable operating conditions by treating real “produced water” generated during oil extraction activities. The developed process consists of an initial acidification, followed by the dosage of BAL and, then, by the addition of Ca(OH)2. The best removal performances were obtained by setting the initial pH at 1 and reaching a final value of 11 through the addition of Ca(OH)2. Boron abatement rapidly grew in response to the increase of bottom ash leachate dosage up to a dose of 20 mL/L, beyond which the removal yield showed an asymptotic trend. The process proved to be very fast reaching the steady state within 10 min and the removal trends were accurately described by a pseudo-second order kinetic law. The temperature had a positive effect on the process performance when using low BAL dosages for values up to 40 °C. Beyond this temperature there was a deterioration in the boron removal regardless of the dose of bottom ash leachate. An abatement efficiency close to 90 % was reached at T = 20 °C by dosing in sequential steps five aliquots of an overall BAL dosage of 20 mL/L. The characterization of precipitate proved the coexistence of multiple compounds in both crystalline and amorphous form. The treated water had very low concentrations of metallic ions.