Determination of protolytes by flow procedures : applications to liquors from the hydrometallurgical nickel industry

Sammanfattning: The general intention of this work is to contribute inreplacing complicated and time consuming titration methods foracid/base determination in cases where a rapid answer is morevaluable than a very high accuracy. The versatility of FlowInjection Analysis (FIA) is utilised for the determination ofprotolyte compounds, considering their role in our daily lifeas well as in science and technology. An overview of flowprocedures aiming at this task is given.A procedure classified as a single point FIA titration hasbeen developed. A two line manifold is used. The protolytesample is injected into a carrier, which merges and reacts witha reagent (buffer/indicator). A theoretical model for the exactrelationship between the measured peak height (absorbance) andthe injected concentration has been developed.A rational methodology for selecting the proper reagentcomposition for such systems was devised. With non-linear curvefitting based on a practical simplification of the completemodel good results were obtained over acceptable concentrationranges.The described procedure was successfully tested on twoanalytical problems related to the hydrometallurgical nickelextraction industry. The determination of sulphuric acid inliquors containing a high concentration of hydrolyzable metals,from the acidic technology, was developed using a reagentmixture comprising sodium sulphate and methyl orange.Determinations of total ammonia and carbon dioxide in leachingsolutions used in the ammoniacal process, were also performed.Total alkalinity (total ammonia) was measured using a mixtureof acetic acid and bromophenolblue. For the strong alkalinity aborit acid/cresol red system was used as reagent. The totalcarbon dioxide was computed from the differente between totaland strong alkalinity.KEYWORDS:Flow Injection Analysis; FIA; Flow procedures;Acids; Bases; Indicators; Spectrophotometric; Industrialliquors; Sulphuric Acid; Ammonia; Carbon Dioxide; Non-linearcalibration.