INTEGRATED BORON REMOVAL AND FLOCCULATION PROCESS FOR TREATING FRACTURING WASTEWATER

Abstract

An integrated boron removal and flocculation process for treating fracturing wastewater is disclosed. The process comprises: adjusting the pH of the fracturing flowback liquid to be treated to become alkaline and adding thereto an oxidant to carry out a reaction for a certain time period, so that the state of the boron present in the liquid is changed; and then adding a barium salt to the resulting reaction mixture to carry out a further reaction between the barium salt and the boron in the changed state to produce a precipitate. The stability of the flowback liquid is deteriorated by the addition of the oxidant. Suspended solids in the flowback liquid can be removed through adsorption, wrapping, and then settling by the action of the precipitate (a barium salt). The process integrates boron removal and flocculation and enables a boron removal rate of 80% or greater. The contents of the suspended solids and oil present in the fracturing flowback liquid after filtration each can be lowered to less than 5.0 mg/L.

Claims

1. An integrated boron removal and flocculation process for treating fracturing wastewater, comprising steps of: adjusting a pH level of the fracturing flowback liquid to be treated with an alkali to a range of 8.5 to 10.0; adding an oxidant to the flowback liquid after pH adjustment to carry out a reaction at room temperature for 30 to 120 minutes; adding a barium salt to the reaction mixture resulting from the reaction to carry out a further reaction at room temperature for 30 to 120 minutes; and allowing the reaction mixture resulting from the preceding step to stand still and settle before filtration via a filtration unit.

2. The process according to claim 1, wherein the alkali is a 10 to 30 wt. % aqueous sodium hydroxide or potassium hydroxide solution.

3. The process according to claim 1, wherein the barium salt is barium chloride or barium nitrate.

4. The process according to claim 1, wherein the ratio of the barium salt used to the fracturing flowback liquid to be treated is 100-150 mg:1 L.

5. The process according to claim 1, wherein the oxidant is a 25 to 30 wt. % aqueous hydrogen peroxide solution or a 12 to 15 wt. % aqueous sodium hypochlorite solution.

6. The process according to claim 1, wherein the volume of the oxidant used is 0.15 to 0.5% of that of the fracturing flowback liquid to be treated.

7. The process according to claim 1, wherein the fracturing flowback liquid to be treated has a boron content of 100 to 200 mg/L.

8. The process according to claim 1, wherein the fracturing flowback liquid to be treated is a guar gum base liquid or a guar gum-polymer base liquid, wherein the polymer is partially crosslinked polyacrylamide with a viscosity-average molecular weight of 12,000,000 to 18,000,000; and the ratio of the guar gum to the polymer is 3:1 to 5:1 by weight.

9. The process according to claim 1, wherein the stand still and settling step lasts for 20 to 40 minutes.

10. The process according to claim 1, wherein the filtration unit is formed by two filters, in series, selected from the group consisting of walnut shell, quartz sand, and modified fibrous ball filters.

11. The process according to claim 3, wherein the ratio of the barium salt used to the fracturing flowback liquid to be treated is 100-150 mg:1 L.

12. The process according to claim 5, wherein the volume of the oxidant used is 0.15 to 0.5% of that of the fracturing flowback liquid to be treated.

Description

DETAILED DESCRIPTION

[0026] The embodiments of the present disclosure will be further described in detail with reference to examples, but the disclosure is not limited to these examples.

Example 1

[0027] 1000 mL of guar gum base fracturing flowback liquid (water base liquid) was taken and the pH was adjusted to 10 using 30 wt. % aqueous sodium hydroxide solution. 2 mL of 30 wt. % aqueous hydrogen peroxide solution was then added to the liquid to carry out a reaction at room temperature for 120 minutes. Thereafter, 150 mg of barium chloride was added to carry out a further reaction at room temperature for 30 minutes. The resulting reaction mixture was allowed to stand still and settle for 30 minutes, and then was filtered via one walnut shell filter and one quartz sand filter arranged in series. It was found that the boron content in the liquid was reduced from 154 mg/L to 28 mg/L with a boron removal rate of 80%, and the suspended solids and oil contents were reduced from 85 mg/L and 60 mg/L to 5.0 mg/L and 3.0 mg/L, respectively.

Example 2

[0028] 1000 mL of guar gum-polymer (polyacrylamide with a viscosity-average molecular weight of 12,000,000; mass ratio of the guar gum to the polymer=3:1) base fracturing flowback liquid (water base liquid) was taken and the pH was adjusted to 9.5 using 20 wt. % aqueous sodium hydroxide solution. 5 mL of 12 wt. % aqueous sodium hypochlorite solution was then added to the liquid to carry out a reaction at room temperature for 90 minutes. Thereafter, 120 mg of barium nitrate was added to carry out a further reaction at room temperature for 40 minutes. The resulting reaction mixture was allowed to stand still and settle for 20 minutes, and then was filtered via one quartz sand filter and one modified fibrous ball filter arranged in series. It was found that the boron content in the liquid was reduced from 143 mg/L to 14.1 mg/L with a boron removal rate of 90%, and the suspended solids and oil contents were reduced from 106 mg/L and 80 mg/L to 4.0 mg/L and 2.0 mg/L, respectively.

Example 3

[0029] 1000 mL of guar gum base fracturing flowback liquid (water base liquid) was taken and the pH was adjusted to 8.5 using 10 wt. % aqueous sodium hydroxide solution. 4 mL of 25 wt. % aqueous hydrogen peroxide solution was then added to the liquid to carry out a reaction at room temperature for 90 minutes. Thereafter, 100 mg of barium chloride was added to carry out a further reaction at room temperature for 100 minutes. The resulting reaction mixture was allowed to stand still and settle for 30 minutes, and then was filtered via one walnut shell filter and one modified fibrous ball filter arranged in series. It was found that the boron content in the liquid was reduced from 103 mg/L to 9.7 mg/L with a boron removal rate of 90%, and the suspended solids and oil contents were reduced from 110 mg/L and 108 mg/L to 6.0 mg/L and 4.0 mg/L, respectively.

Example 4

[0030] 1000 mL of guar gum-polymer (polyacrylamide with a viscosity-average molecular weight of 18,000,000; mass ratio of the guar gum to the polymer=5:1) base fracturing flowback liquid (water base liquid) was taken and the pH was adjusted to 10 using 30 wt. % aqueous potassium hydroxide solution. 3 mL of 15 wt. % aqueous sodium hypochlorite solution was then added to the liquid to carry out a reaction at room temperature for 30 minutes. Thereafter, 130 mg of barium nitrate was added to carry out a further reaction at room temperature for 90 minutes. The resulting reaction mixture was allowed to stand still and settle for 40 minutes, and then was filtered via one walnut shell filter and one modified fibrous ball filter arranged in series. It was found that the boron content in the liquid was reduced from 123 mg/L to 11.7 mg/L with a boron removal rate of 90% or greater, and the suspended solids and oil contents were reduced from 97 mg/L, and 68 mg/L, to 5.0 mg/L, and 2.0 mg/L, respectively.

[0031] The above are only preferred embodiments of the present disclosure. It will be understood that various modifications and improvements may be made without departing from the scope and principle of the disclosure.