In one of the chemical reaction that I do, the waste product coming is sodium sulfide(Na2S) dissolved in water and it has a deep yellow color. Is there any way to separate the Na2S that was dissolved in water to some other useful solid products or convert to another chemical product through some easy steps that does not involve the supply of heat.Also,is there another use of the dissolved sodium sulfide in water?Somewhere I read that it can be used in paper and fertilizer industries.
Thanks,
Dr.Kumar
Mr Subhash Chandra Basu has replied to the similar question and it is
he heating is the cheapest and simplest way. One can separate without any lab.
But in industry a different way is followed:
Many industrial wastewaters, particularly those associated with mining and mineral processing, contain high concentrations of sulfate.
The most common method for removing high concentrations of sulfate from water is through addition of hydrated lime (Ca(OH)2), which precipitates calcium sulfate:
Na2SO4 + Ca(OH) 2 => CaSO4 + 2 NaOH
At industrial level it carried out in steps
Step 1 -- Initial Sulfate Precipitation
For wastewater with a high metals content and a sulfate concentration greater than 8000 mg/L, hydrated lime is used initially to precipitate most of the sulfate as gypsum. This precipitation occurs at a pH below which the metals will precipitate. Over 80 percent of the sulfate in many wastewaters can be precipitated prior to metals precipitation in order to minimize the volume of hazardous sludge.
Step 2 -- Metal Hydroxide Precipitation
Wastewater with an initial sulfate concentration below 8000 mg/L, or which has already been treated using gypsum precipitation, is adjusted to a pH of 10.5 with hydrated lime. This removes metals as hydroxides and precipitates more gypsum, so approximately 2000 mg/L of sulfate remains in solution. As with the initial sulfate precipitation step, a mixing time of 40 to 60 minutes is adequate.
Step 3 -- Final Sulfate Precipitation
The next step of the process is removal of sulfate to the desired concentration. The wastewater pH is increased to approximately 11.5 with hydrated lime. At this stage, the proprietary reagent is dosed at the rate of approximately one pound of reagent per pound of sulfate. The reagent combines with soluble sulfate to form an ettringite precipitate. During ettringite precipitation, contaminants such as nitrate, chloride, fluoride, boron and metals may be incorporated into its structure. Insoluble gypsum will interfere with this reaction if not removed in a previous step.
Step 4 -- pH Reduction/Recarbonation
It is often necessary to lower the effluent pH to meet discharge criteria. If treated water is to be reused in the plant, the pH should be reduced to prevent deposition of hard carbonate scale on filters and distribution piping. Recarbonation (addition of carbon dioxide) is the process typically used for pH reduction.
In the Cost-Effective Sulfate Removal (CESR) process used by Hydrometrics, a proprietary reagent is added after standard lime treatment to precipitate a compound called ettringite, which can be removed using a clarifier and filter press. Sulfate, heavy metals and other contaminants may be removed in the process, which generates no liquid waste.
The CESR process is simpler and less expensive than other sulfate-removal technologies such as reverse osmosis, ion exchange or sodium aluminate addition, and is more effective than standard lime precipitation. This process is a true reduction of total dissolved solids (TDS) in that all chemicals added for treatment are precipitated during the reactions.
If i will come to know any other way or process then definitely i will share with you.
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