H-Acid (1-amino-8-naphthol-3,6-disulfonic acid) is a key intermediate used in the production of acid dyes, direct dyes, and reactive dyes for wool and cotton textile dyeing. However, the H-acid wastewater generated during the crystallization mother liquor stage has long been one of the most critical challenges restricting the development of the dye intermediate industry. Effective treatment of this wastewater has become increasingly urgent. How to efficiently recover H-acid and valuable organic compounds from wastewater remains a major issue that enterprises must address.

This type of wastewater exhibits the typical characteristics of “Four Highs”:

High Concentration – COD values typically reach 20–50 g/L, accompanied by extremely high color intensity.
High Acidity – pH values are generally around 2.
High Salinity – containing large amounts of inorganic salts such as sodium sulfate and ammonium sulfate.
High Biological Toxicity – carrying significant quantities of structurally stable naphthalene-based organic compounds that are difficult to degrade naturally.

Traditional treatment technologies often struggle in this challenging application:

Macroporous resin adsorption offers limited removal efficiency; chemical oxidation processes involve high operating costs and may generate secondary pollution; catalytic wet oxidation requires substantial energy consumption; and the high-salt environment directly inhibits the biological activity of activated sludge systems. As wastewater discharge regulations become increasingly stringent, many conventional treatment methods can no longer meet current environmental standards, exposing enterprises to significant risks of production suspension and mandatory rectification.

Integrated “Two-Stage Extraction and One-Stage Stripping” Process with Centrifugal Extractors

Drawing on years of technological expertise, Zhengzhou Tiei Extraction has developed an integrated “Two-Stage Extraction and One-Stage Stripping” process based on the CWL-M Series Centrifugal Extractor. Built upon the principle of complexation extraction, this process fully utilizes the centrifugal extractor’s advantages of rapid mixing and fast phase separation, transforming H-acid wastewater pretreatment from a high-cost burden into a resource recovery platform capable of creating additional value.

1.pH Adjustment and Extractant Preparation
The treatment process begins with precise pH adjustment of the H-acid wastewater to the optimal extraction range (approximately pH 0.5–2.0) in order to maximize extraction efficiency. Meanwhile, a high-performance extractant specifically designed for H-acid mother liquor is prepared and introduced into the system. The extractant is typically formulated from tertiary amine solvents, diluents, and modifiers at optimized proportions.

2.Two-Stage Cross-Current Extraction (“Two-Stage Extraction”)
The conditioned wastewater and extractant are fed into the CWL-M Series Centrifugal Extractor at an optimized ratio. Inside the extractor, the high-speed rotating drum generates a powerful centrifugal force, enabling rapid mixing and highly efficient mass transfer between the aqueous phase and the organic phase. Naphthalene sulfonic acid compounds contained in the wastewater are selectively transferred from the aqueous phase into the organic extractant phase. After the first extraction stage, the wastewater proceeds to a second cross-current extraction stage to further enhance the removal efficiency of organic contaminants.
Experimental results show that after the two-stage cross-current extraction process, the wastewater COD can be reduced from tens of thousands of mg/L to below 1,000 mg/L, the residual H-acid content can be lowered to less than 0.1%, and the wastewater color becomes nearly colorless.

3.One-Stage Stripping
The loaded organic phase containing extracted organics is then transferred to the stripping section. Within the centrifugal extractor, it is brought into full contact with an alkaline stripping solution. The extracted organic compounds are transferred from the organic phase into the stripping solution. The resulting high-concentration stripping liquor can subsequently be concentrated through evaporation and further processed into naphthalene-based superplasticizers used in concrete admixture production, thereby converting waste into valuable products. Meanwhile, the extractant is regenerated and recycled back to the extraction stage, achieving an extractant recycling efficiency of over 99%.

Through this closed-loop process, valuable organic compounds contained in H-acid wastewater are efficiently recovered. The raffinate (aqueous phase) after extraction contains only trace amounts of residual organic matter and can be smoothly transferred to the biological treatment stage for further purification.

Advantages of the CWL-M Centrifugal Extractor

As specialized equipment for H-acid recovery, the superior performance of Zhengzhou Tiei Extraction's CWL-M Series Centrifugal Extractor in H-acid wastewater treatment stems from its fundamentally different technical architecture compared with conventional extraction equipment, as well as years of continuous engineering optimization. As a manufacturer of centrifugal extraction equipment, Zhengzhou Tiei Extraction has developed comprehensive technical customization specifically for the extreme operating conditions encountered in dye intermediate wastewater treatment.

1.Designed for Strong Acid and High-Salt Conditions, Ensuring Long-Term Stable Operation
H-acid wastewater typically has a pH value as low as 0.5 and a salt content of up to 14%, placing extremely stringent demands on equipment corrosion resistance. Key components of the CWL-M Centrifugal Extractor are manufactured from special alloys or high-performance composite materials, enabling the equipment to withstand severe chemical corrosion under strong acid and high-salt conditions over extended periods. This significantly extends equipment service life while reducing replacement and maintenance costs.

2.Efficient Mass Transfer + Rapid Phase Separation Greatly Reduce Processing Time
Compared with conventional mixer-settlers that require residence times of tens of minutes, the CWL-M Centrifugal Extractor utilizes a high-speed centrifugal force field to achieve complete mixing and thorough phase separation within just a few seconds. For the same processing capacity, the equipment provides extremely short residence time, significantly higher treatment efficiency, and a much smaller installation footprint than traditional extraction equipment.

3.Extremely Low Power Consumption Significantly Reduces Operating Costs
To address the challenge of high energy consumption in industrial wastewater treatment, the CWL-M Series Centrifugal Extractor has undergone systematic power optimization. Taking the CWL650-M model as an example, the actual operating power consumption of a single unit is only 4 kW. Compared with conventional annular centrifugal extractors, the CWL-M Series consumes only 10%–30% of the power required by traditional equipment. In industrial applications treating hundreds of thousands of tons of wastewater annually, the resulting electricity cost savings are highly significant.

4.Fully Enclosed Continuous Operation for Safety, Environmental Protection, and Regulatory Compliance
The entire system is capable of fully enclosed continuous operation. The extractant exhibits low volatility, effectively eliminating organic solvent emissions and minimizing on-site odor issues. At the same time, the system supports precise automated control and requires minimal operator intervention, significantly reducing labor intensity and human error while ensuring stable and reliable effluent quality.

5.Minimal Extractant Loss Enables a Low-Cost Recycling System
Benefiting from its excellent phase separation performance, the CWL-M Centrifugal Extractor effectively minimizes extractant losses caused by entrainment during separation. Combined with an efficient solvent recovery system, the extractant can be recycled and reused over long periods, substantially reducing the overall chemical consumption cost per ton of wastewater treated and truly achieving the goal of low-cost wastewater treatment.

Application Case

H-Acid Wastewater Treatment Project at a Chemical Plant

Project Background: The chemical plant generated H-acid wastewater with an initial COD value of up to 30,000 mg/L, an H-acid concentration of approximately 5%, and a salt content of 14%. The wastewater appeared dark brown to black in color, with a treatment capacity of 15 m³/h.

Process Selection: The project adopted the CWL650-M Centrifugal Extractor supplied by Zhengzhou Tiei Extraction, utilizing the integrated “Two-Stage Extraction and One-Stage Stripping” process.

Operational Results: The wastewater COD level dropped below 1,000 mg/L (with a 96% removal rate), and the H-acid content fell below 0.1% (with a 98% extraction rate). The treated wastewater was nearly colorless and transparent, achieving a 95% color removal rate, and was suitable for direct transfer to the biochemical treatment stage. Following stripping with a 10% NaOH solution, the residual H-acid in the organic phase was less than 0.5%, enabling long-term recycling of the extractant.

Customer Feedback: “The equipment operates reliably with a high degree of automation. It not only solved our wastewater compliance challenges but also enabled resource recovery from waste, generating significant environmental and economic benefits for our company.”

With the CWL-M Centrifugal Extractor at its core, solvent extraction technology is becoming the preferred solution for H-acid wastewater pretreatment due to its five key advantages: high efficiency, low energy consumption, compact footprint, environmental friendliness, and resource recovery capability. When integrated with downstream processes such as MVR (Mechanical Vapor Recompression) evaporation and advanced biological treatment, centrifugal extraction pretreatment provides a solid technical foundation for establishing a complete resource-recovery closed-loop treatment system for H-acid wastewater.

Zhengzhou Tiei Extraction Technology Co., Ltd. is a professional manufacturer of centrifugal extraction equipment, providing comprehensive solutions covering process verification, laboratory testing, pilot-scale validation, industrial-scale equipment supply, and long-term operational technical support. We help H-acid producers and related enterprises achieve both environmental compliance and economic benefits at the lowest possible overall operating cost.
Email: sales@tieiextraction.com
Whatsapp: +86 19069612820