Acid-Resistant NF Membranes Turn Waste into Gypsum

The core bottleneck in titanium gypsum resource utilization is not the surface problem of a huge solid waste volume, but a systematic technical gap formed by difficult impurity control, poor crystal characteristics, outdated conventional processes and missing supporting standards. With years of deep cultivation in membrane technology, Jiuwu Hi-Tech has built a core technical moat with its self-developed acid-resistant nanofiltration membrane, and innovated a coupled process of "membrane integration + neutralization crystallization + low-temperature slow calcination", creating the first complete resource recovery equipment set in China, thoroughly breaking through the shortcomings of conventional technology, achieving efficient conversion of titanium gypsum from industrial solid waste to high-quality building material resources, and providing hard-core technical support for refined and high-value treatment of industrial solid waste.

Solid Waste Treatment Challenges: Three Core Bottlenecks

The conventional approach to titanium gypsum treatment is "end-of-pipe neutralization": acid wastewater is directly neutralized with alkali, and metal ions and sulfuric acid precipitate together with gypsum, with impurities locked inside the gypsum crystals. Once impurities have already mixed into the gypsum, treatment can only rely on washing and calcination for remediation, with limited effect. The main problems are:

Problem 1: Impurities locked inside crystals, low gypsum grade and poor whiteness

High impurity content results in extremely low strength of hemihydrate gypsum after calcination, with limited building material applications; its dosage as a cement retarder is restricted, otherwise the 3-day and 28-day strength of cement is significantly reduced.

Problem 2: Fine crystal size and high free water, high dewatering energy consumption

Conventional process crystal size is only 5-20 μm with free water as high as 35%-50%, making dewatering difficult and resulting in poor mechanical properties.

Problem 3: End-of-pipe neutralization does not reduce by-product output, only relocates the stockpile

Product quality is poor and by-product output is not reduced; end-of-pipe treatment is merely "piling it somewhere else", making large-scale application difficult.

First Complete Equipment Set Implemented: Metal Ion Retention and Recovery, Sulfuric Acid Reuse in Production

Jiuwu Hi-Tech innovatively adopts an upstream process treatment scheme: before gypsum crystallizes and precipitates from titanium dioxide acid wastewater, membrane separation technology efficiently separates metal ions from sulfuric acid, the retained metal ions are recovered as resources, and sulfuric acid permeates through the membrane module for direct reuse in production. This complete titanium gypsum resource utilization equipment set is the first of its kind in China and was shortlisted in the 2025 Jiangsu Provincial Department of Industry and Information Technology "Three Firsts, Two News" proposed recognition list (first-of-its-kind equipment, first batch, first edition, new technology and new product), forming a complete solution of "metal recovery - source carbon reduction - titanium gypsum high-value utilization", with comprehensive performance reaching the international advanced level.

Technical Advantages: Self-Developed Acid-Resistant NF Membrane Builds the Process Barrier

The performance ceiling of the complete equipment set depends on whether the core membrane element can operate stably over the long term under strongly acidic conditions. Titanium dioxide acid wastewater has high acid concentration, many metal impurities and large operating fluctuations; conventional organic nanofiltration membranes are prone to hydrolysis and short service life, making them difficult to apply directly. Jiuwu Hi-Tech's self-developed acid-resistant nanofiltration membrane was developed precisely for these conditions and forms the technical foundation of the entire process.

Advantage 1: Resists strong acid corrosion, adapts to harsh titanium dioxide wastewater conditions

The NF-A membrane can operate stably in strong acid environments such as 30wt% sulfuric acid and 20wt% hydrochloric acid, with MgSO₄ rejection above 97%; under actual titanium dioxide wastewater conditions it delivers high separation precision and stable performance, solving the problems of easy hydrolysis and short life of conventional polyamide membranes.

Advantage 2: 0.6 nm pore size separates acid from metal ions

With a membrane pore size of 0.6 nm, it retains metal ions and allows sulfuric acid to pass through, completing acid-salt separation; the more thoroughly metal ions are removed, the higher the whiteness and purity of the subsequently formed gypsum.

Advantage 3: Fouling resistance and stable flux, low operation and maintenance costs

Long-term operation shows low flux decline, with no need for frequent cleaning or membrane element replacement, long service life and controllable operating costs.

Advantage 4: Membrane integration coupling enables full-component recovery

• The dual-membrane process recovers 100% of metatitanic acid, with recovery rates of titanyl sulfate and ferrous sulfate at 90% or above and desalination above 96%;

• Directed crystallization increases crystal size from 5-20 μm to 60-100 μm, reducing free water below 12%;

• Low-temperature slow calcination at 180°C or below produces building plaster meeting Grade 3.0 of the national standard.

Case Evidence: Full-Process Technology Helps Enterprises Reduce Costs and Increase Efficiency

In a titanium dioxide waste acid and water resource recovery project in Shanghai, Jiuwu Hi-Tech adopted a full-process membrane integration of "ultrafiltration - nanofiltration - neutralization - black mud washing", with a design treatment scale of 2,500 m³/d × 340 d. The special ultrafiltration membrane provides first-stage purification, retaining and recovering suspended metatitanic acid with a recovery rate of 95% or above; the special nanofiltration membrane provides second-stage separation, with ferrous sulfate and titanyl sulfate recovery rates of 95% or above.

Taking an enterprise producing 50,000 tons of titanium dioxide per year as an example: the ultrafiltration stage recovers 125 tons of metatitanic acid annually (annual revenue of RMB 750,000), the nanofiltration stage recovers 20,000 tons of ferrous sulfate heptahydrate annually (annual revenue of about RMB 10 million), the neutralization stage saves 10,000 tons of chemicals annually (annual revenue of about RMB 1.5 million), and landfill fees are reduced by RMB 3 million per year. Combining the three stages, annual economic benefit reaches RMB 15.25 million.

Even more exemplary is the business model innovation: Jiuwu Hi-Tech invests in and builds the project under a BOT (Build-Operate-Transfer) model, providing a new cooperation paradigm for acid wastewater treatment in the titanium dioxide industry and lowering the threshold of environmental investment for enterprises.

Conclusion

Relying on nearly thirty years of membrane technology accumulation, Jiuwu Hi-Tech has achieved a breakthrough from acid-resistant nanofiltration membrane strong-acid separation technology to the first complete titanium gypsum resource recovery equipment set in China, forming a complete closed loop of "metal recovery - source carbon reduction - titanium gypsum high-value utilization". In the future, Jiuwu Hi-Tech will continue to focus on the R&D of acid-resistant, alkali-resistant and fouling-resistant special membrane materials, continuously optimize membrane integration processes, and drive the titanium dioxide, metallurgy, pickling and other industries toward "solid waste reduction, maximum resource utilization and minimum environmental impact", continuously promoting green development of the industry.