Evaluating Ferrous Chloride for Removal of Chromium From Ion‐Exchange Waste Brines

Abstract

Ferrous chloride (FeCl 2 ) added to chromium-laden brines produced by strong base anion (SBA) exchange systems reduces hexavalent chromium (Cr(VI)) to trivalent chromium (Cr(III)) and precipitates the Cr(III) in a mixed chromium-iron hydroxide solid solution. A series of jar tests were conducted in which FeCl 2 was added to synthetic SBA exchange brines. The variables investigated were the initial Cr(VI) concentration, initial pH, and ferrous iron stoichiometric dose. This reduction-coagulation-flocculation (RCF) process was also tested on field brines with various compositions. The RCF process achieved >77% chromium removal efficiency at all tested conditions, except in brines with a bicarbonate matrix. Significant vanadium (V) and arsenic (As) removal (>78 and >49% removal, respectively) was observed in field brines with a chloride or sulfate matrix. Diffuse double-layer modeling suggests that adsorption to the precipitated solids was the predominant removal mechanism of V and As.

Forward Osmosis for Ion Exchange Waste Brine Management

“…Many approaches have been investigated to reduce the volume of waste brine requiring disposal, including novel regeneration approaches, , recycling, ,,− chemical treatment, − biological treatment, ,, photocatalytic techniques, and nanofiltration. − Each of these options has disadvantages, and because IX waste brine is a complex mixture, some approaches are only effective for select contaminants. Thus far, approaches that treat and reuse brine lead to the accumulation of impurities in the regeneration solution. , The most selective demonstrated approach is nanofiltration, which recovers excess sodium chloride (NaCl) but lacks nitrate rejection .…”

Effects of Halides on Organic Compound Degradation during Plasma Treatment of Brines

“…Though the amount of Br – compared to Cl – is relatively consistent in brines (i.e., 0.1–1 mol % Br – , Table S3), the absolute concentrations of halides vary substantially (e.g., 0.007–2 M Cl – , Table S3). ,,,,,,− Therefore, we expanded our experiments to evaluate the effect of halides at different concentrations but at a constant ratio of Br – to Cl – (i.e., 0.1–2 M Cl – with 1 mol % Br – ). The inclusion of halides at concentrations higher than 0.5 M Cl – and 5 mM Br – increased the degradation rate of para -hydroxybenzoate by 2- to 4-fold relative to ClO 4 – at the same ionic strength and conductivity (Figure f).…”

“…Consistent with our expectation, both degradation rates of organic compounds (Figure a) and hypohalous acid concentrations (Figure S19) were comparable in the presence of these anions at their median concentrations reported in brines (i.e., 0.25 M SO 4 2– , 0.08 M NO 3 – , Table S3). ,,,,,,− …”

“… ,,− Like Cl – and Br – , additional constituents (i.e., sulfate, SO 4 2– ; nitrate, NO 3 – ; carbonates; organic matter) were added at brine-relevant concentrations (Table S3). ,,,,,,− Some of these constituents have known reactivities with the reactive species of interest (Table S5). ,,,− All salts used in this study contained sodium as the cation.…”

“…In experiments containing both Br – and Cl – , Br – was added at 1 mol % Cl – , corresponding to molar ratios reported in brines (i.e., 0.1–1 mol %, Table S3). ,,,,,,− When isolating the effect of Cl – alone, different experiments were performed with both lower-purity (i.e., ≥99.0%, 0.004 mol % Br – , Text S3 , and Figure S4) and higher-purity (99.999%) Cl – reagents as indicated in corresponding figures. When Br – was added, lower-purity Cl – was used because the trace Br – in the Cl – reagent is negligible relative to the added Br – .…”