JPS5879591A - Method of preparing sulfide in aqueous system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a convenient method for controlling sulfides and other reducing agents in aqueous solutions using a compact form of peroxygen with a defined dissolution rate.

Hydrogen peroxide is known to be useful for controlling hydrogen sulfide in aqueous solutions. p) (When used at 7 or less, hydrogen peroxide oxidizes hydrogen sulfide to elemental sulfur more economically than sulfate. It oxidizes sulfide in wastewater to elemental sulfur and eliminates odors from hydrogen peroxide. Applications of this hydrogen peroxide to reduce sulfides have been published in U.S. Pat. Nos. 470-098 and 3,550,067. The cost of the system is considerable.Also, since it is undesirable to dispose of wastewater containing insoluble elemental sulfur, it is necessary to filter or coagulate the sulfur from the solution before disposing of the treated wastewater.

Hydrogen peroxide is well known as an oxidizing and reducing agent. It acts most effectively as an oxidizing agent in alkaline solutions. Therefore, when using hydrogen peroxide or an adduct compound of hydrogen peroxide to reduce the chemical oxygen demand in solution, p
It is better to raise H to 7 or higher. If the sulfide is completely oxidized to sulfate by hydrogen peroxide, the solution pH should be at least 8.
It is necessary to do so. Since many wastewaters have a pH of 7 or less, additional equipment and chemicals are required to continuously raise the pH to a reasonable range and keep the hydrogen peroxide in solution, increasing the cost of this process.

Addition of a solid alkaline hydrogen peroxide addition compound, such as sodium peroxide carbonate or sodium perphosphate, simultaneously provides pH adjustment of the solution and hydrogen peroxygen that oxidizes sulfides to sulfates. However, it is difficult to feed the system with powder or crystals. It is difficult when the scale is small. Furthermore, the available alkalinity and active oxygen produced by this compound will not be in optimal proportions for both solution pH adjustment and oxidation of sulfide to sulfate.

The present invention overcomes the above-mentioned drawbacks by compressing the solid peracid concentrate, optionally with additives, into a solid form with suitable dissolution rates. If a solid form is dissolved in this way, the simultaneous K
It becomes a pre-measured chemical that adjusts the pH and produces oxidizer 9 over a period of time.

In the present invention, a solid addition compound of hydrogen peroxide, such as sodium carbonate peroxide or sodium peroxide, is physically compressed into a form that provides the necessary alkalinity and active oxygen to the solution on a time basis. This eliminates the need for the use of weighing equipment to supply chemicals that constantly oxidize the sulfide in solution to sulfate. Either sodium peroxide carbonate or sodium perphosphate can be compression molded alone or with additives to control the rate of dissolution and provide the desired chemical balance.

The size and shape of the compression molded article can be varied to further control the rate of dissolution. Tablets are particularly convenient for small-scale trials. However, for a more uniform rate of dissolution, a cylindrical shape with concentric holes can be used since the overall surface shape remains constant during dissolution. For this purpose, the term “tablet” also includes any convenient form*
It's the taste.

Tablet making or molding is carried out using conventional methods and equipment, with or without the use of additives or excipients. However, it is important that the safety and suitability of the formulation be considered. Additives provide a variety of effects on storage or performance. For example, very slowly dissolving additives can be used to reduce the rate of dissolution of tablet products. Inert additives can also be used to dilute active oxygen moieties when small amounts are required. Alkaline additives may be used to raise the pH of particularly acidic wastewater, and colorants or fragrances may be added for aesthetic or personal reasons. The use of other additives for storage stability or easier disposal from the press will be apparent to those skilled in the art.

For practical use, additives need to be inexpensive and non-oxidizable. Efficacy data for two representative additives used to reduce the dissolution rate of sodium peroxide carbonate is shown in the Examples.

One tablet with a diameter of approximately 29 W and a thickness of 15 m is poured into 9 liters of water at ambient temperature.
The dissolution rate was measured in a mesh basket placed just below the water surface of a 1 t beaker containing 50 liters of water. A stir bar was rotated at the bottom of the beaker at a speed slightly slower than that to create the vortex. The dissolution time was observed and recorded. Hydrogen peroxide concentration was measured by selenium sulfate titration.

The sulfide concentration and flow rate of a given wastewater must be commensurate with the rate at which active oxygen is released along with the pH-adjusting alkali and the desired operating time between tablet changes.

There are many mechanical devices that introduce sodium peroxide and carbonate tablets into wastewater. One very simple method of gravity-flow system is to immerse a portion of a wire mesh cylinder filled with tablets in a liquid stream. In pressure systems such as Force Mains, tablet feeding is performed using a bypass with a valve. By using bypass, the process is also not interrupted during tablet replenishment. During operation, drug delivery can be controlled by a combination of tablet exposure and drainage flow rate around the tablet.

The life cycle of the charge is determined based on the tablet size used by adjusting parameters to provide the desired sulfide control early in the operation. Depending on the length of the desired cycle, the required length of the loaded tablet can be increased or decreased.

Example 1 Sodium peroxide carbonate tablets were produced using a 29 mm diameter die at a compression pressure of 95 MPa. The tablets contained sodium peroxide carbonate only 15F or it with 10% 115% or 20% carboxymethylcellulose or methylcellulose. The dissolution time of a tablet (in minutes) is approximately calculated by the following formula:
It was found that it is expressed in the % formula % (48 (where A is the percentage of either carboxymethyl cellulose or methyl cellulose in the formulation).

Example 2 Sodium perphosphate tetrahydrate alone, carboxymethylcellulose (CMC), methylcellulose (MC
), sodium carbonate (soda ash), and sodium chloride to make tablets. Tablet strength is CMC or MC 5
It was found that the addition of -20% improved this and the addition of soda ash or sodium chloride reduced it. The dissolution rate decreased with increasing CMC or MC. When 10 weight or more of CMC is added, dissolution is extremely slow. MC is a good binder like CMC, but dissolves more quickly and forms tablets.

The concentration of sodium borate in the wire ranges from 101% to 4.
As the pH of the tap water increased to 0-, the pH of the tap water increased from &7 to 1α2.

The largest variation was from 101% to n and sl. At similar concentrations, the pH of crude sewage increased from &3 to 11.1.

The perborate tablets reacted with a 7-8 ppm sulfide solution in tap water and oxidized the sulfide to sulfate within 15 minutes. This time was initially observed in wastewater samples containing about 7 ppm sulfide.

Table 1.

0 3! 11'0
40 4815
65 7020
135 140 Spicy 15F sodium carbonate tablets mixed with carboxymethylcellulose (CMC) or methylcellulose (MC).

Claims (1)

[Claims] 1. A method in which both an alkaline substance and hydrogen peroxide are added to a solution on a time basis and the solution is continuously oxidized with alkaline hydrogen peroxide to convert aqueous sulfide ions to sulfate,
An improved method characterized in that the solid alkaline hydrogen peroxide addition compound is compressed into a molded form to alter the rate of dissolution of said compound to adjust the rate of addition of the alkaline material and the rate of addition of hydrogen peroxide. 2. The method according to claim 1, wherein the hydrogen peroxide addition compound is a compound selected from the group consisting of sodium peroxide carbonate or sodium perphosphate tetrahydrate. 5. The method according to claim 1 or 2, wherein the improved method further comprises a speed-altering compound in the molded form. 4. Claim 3, wherein the molded form contains up to 25-carboxymethyl cellulose as a speed-changing compound.
The method described in section. 5. A method according to claim 5, wherein the molded form contains up to 25-methylcellulose as the rate-altering compound. 4. The method of claim 3, wherein the molded form contains up to 25% IJ carbonate as a speed modifying compound. 2. A method according to claim 3, wherein the molded form contains up to 25% sodium chloride as a speed modifying compound. a. In a method in which both an alkaline substance and hydrogen peroxide are added to a solution on a time basis and the solution is continuously oxidized with alkaline hydrogen peroxide to convert aqueous sulfide ions to sulfate, (
a) Sodium peroxide carbonate and sodium perphosphate 4
a compound selected from the group consisting of hydrates, (b) an additional base, and (c) a rate-modifying compound, by compressing the mixture into a molded form to modify the rate of dissolution of said mixture. An improved method characterized by adjusting the addition rate and the alkali to hydrogen peroxide ratio. 2. The method of claim 8, wherein base (b) comprises up to 25% sodium carbonate. 10. The method of claims 8 and 9, wherein the 1α rate-altering compound (C) is a compound selected from the group consisting of carboxymethylcellulose and methylcellulose.