Sulfide Ion Removal from Sodium Hydroxide Solution by Ozonation/Adsorption Method

One of issues preventing utilization of sodium hydroxide, as H2S absorbent in this oil/gas industries, is its recovery, because of an irreversible reaction between NaOH and H2S. In this work, ozone and natural zeolite (clinoptilolite) were used for oxidation of sulfide to sulphate ions and adsorption of sulfate ions from alkaline solution, respectively. A synthetic solution of sodium sulfide in sodium hydroxide was prepared. The effect of three operating variables at three levels including ozonation time, hydrogen peroxide dosage, and initial concentration of sodium sulfide was investigated on conversion of sulfide ion to sulfate ion. The design of experiments was performed utilizing response surface method (RSM) in Design Expert software to find optimum condition of oxidation process. Under optimum condition, i.e., ozonation time: 60 min, hydrogen peroxide dosage: 5 mL and sodium sulfide concentration: 0.03 M, a conversion 72.11% was achieved. In the next step of experimental runs and for the removal of produced sulfate ion in oxidation step, an adsorption process using natural zeolite and surface modified zeolite with barium chloride was applied. The highest adsorption efficiency of sulfate ion (91%) was achieved at the highest level of modified zeolite dosage (8 g zeolite/100 mL of solution). Total removal efficiency 65.7% was reported in whole process of oxidation-adsorption, whereas no significant changes in pH were observed. The present method could be a notable alternative to replace ethanol amines with NaOH solution in oil and gas industries.