Industrial Water Sulphate Removal via pH-Adjusted Electrocoagulation

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Solution Overview

Problem

Current methods for removing sulphate and metals like calcium from industrial waters are limited in effectiveness, as they either fail to decrease sulphate concentrations significantly or introduce secondary toxic effects, and existing electrocoagulation techniques are not well-suited for high sulphate concentrations.

Innovation Solution

A method involving initial pH adjustment of industrial waters with calcium compounds to form a sludge containing gypsum and metal hydroxides, followed by electrocoagulation using aluminium or iron-aluminium anodes to precipitate sulphate as ettringite, with a balancing step to optimize precipitation conditions, allowing for complete or partial removal of sulphate and metals.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If controlled gypsum precipitation is used to remove sulphate, then sulphate concentration decreases, but gypsum precipitation causes scaling of coating and surface of process equipment

Engineering Contradiction:

Improvesulphate concentrationVSAvoidscaling of process equipment

Core Design Contradiction:

Quantity of substanceVSObject-affected harmful factors

Solution Approach 1:

The patent changes the chemical parameters by adjusting pH to specific ranges (9.5-11.5 for first precipitation, 6.5-8.5 for second precipitation) and controlling calcium-to-sulphate ratios to precipitate sulphate as gypsum while preventing equipment scaling through controlled crystallization conditions

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent divides sulphate removal into two separate precipitation stages: first precipitation removes bulk sulphate at high pH, then second precipitation removes remaining sulphate at adjusted pH, with intermediate filtration between stages to prevent scaling

Inventive Principle:

Principle #1Segmentation

2Quantity of substance

If membrane separation is used to remove dissolved sulphate, then sulphate concentration decreases, but the method has high operational cost and technical limitations

Engineering Contradiction:

Improvesulphate concentrationVSAvoidoperational cost

Core Design Contradiction:

Quantity of substanceVSEase of manufacture

Solution Approach 1:

The patent replaces mechanical membrane separation with chemical precipitation processes using pH adjustment and calcium compound addition, which are simpler, more reliable, and have lower operational costs while achieving comparable or better sulphate removal

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Quantity of substance

If electrocoagulation is used with low sulphate concentrations, then sulphate removal is achieved, but the method is not suitable for high sulphate concentrations in industrial waters

Engineering Contradiction:

Improvesulphate concentrationVSAvoidapplicability to high sulphate concentrations

Core Design Contradiction:

Quantity of substanceVSAdaptability or versatility

Solution Approach 1:

The patent performs preliminary pH adjustment and calcium compound addition before electrocoagulation to pre-precipitate bulk sulphate as gypsum, reducing the sulphate load to levels suitable for electrocoagulation and enabling the method to handle high initial sulphate concentrations effectively

Inventive Principle:

Principle #10Preliminary action

4Quantity of substance

If sulphate is biologically reduced, then sulphate is removed from water, but toxic H2S is produced causing secondary toxic effects

Engineering Contradiction:

Improvesulphate concentrationVSAvoidtoxic H2S production

Core Design Contradiction:

Quantity of substanceVSObject-generated harmful factors

Solution Approach 1:

The patent converts the potential harmful biological reduction pathway into a beneficial chemical precipitation process by using controlled pH adjustment and calcium compounds to precipitate sulphate as non-toxic gypsum, avoiding H2S generation entirely while still achieving sulphate removal

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Data Source

PatentEP2935126B1Method of treating industrial water

Publication Date: 2020.03.25 OUTOTEC FINDLAND OY

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AI summary

The invention relates to a method and apparatus of removing sulphate and soluble metals such as calcium from water. The invention relates also to a method of controlling the method. The method comprises steps of a) precipitating a first part of sulphate of the water by contacting the water with a first calcium compound and adjusting pH of the water to 10.5 or higher so as to form a first sludge containing gypsum and metal hydroxides, b) subjecting the first sludge containing gypsum to electrocoagulation for precipitating a second part of sulphate as ettringite, and for precipitating calcium-aluminium/iron-sulphate hydroxides, c) conducting the sludge formed in steps a) and b) to solid-liquid separation for separating precipitated solids from the water, d)neutralizing the water received from step c) to provide water decreased in sulphate and soluble metal such as calcium content.