headerdrawing1.jpg (96365 bytes)

Sulphuric Acid on the WebTM Technical Manual DKL Engineering, Inc.

Knowledge for the Sulphuric Acid Industry Line.jpg (1139 bytes)

Sulphuric Acid on the Web

Introduction
General
Equipment Suppliers
Contractor

Instrumentation
Industry News
Maintenance
Acid Traders
Organizations
Fabricators
Conferences

Used Plants
Intellectual Propoerty
Acid Plant Database
Market Information
Library

Technical Manual

Introduction
General

Definitions
Instrumentation
Plant Safety
Metallurgial Processes
Metallurgical
Sulphur Burning
Acid Regeneration
Lead Chamber
Technology
Gas Cleaning
Contact
Strong Acid
Acid Storage
Loading/Unloading

Transportation
Sulphur Systems
Liquid SO2
Boiler Feed Water
Steam Systems

Cooling Water
Effluent Treatment
Utilities
Construction
Maintenance
Inspection
Analytical Procedures
Materials of Construction
Corrosion
Properties
Vendor Data

DKL Engineering, Inc.

Handbook of Sulphuric Acid Manufacturing
Order Form
Preface
Contents
Feedback

Sulphuric Acid Decolourization
Order Form
Preface
Table of Contents

Process Engineering Data Sheets - PEDS
Order Form
Table of Contents

Introduction

Bibliography of Sulphuric Acid Technology
Order Form

Preface
Contents

Sulphuric Acid Plant Specifications
 

Google Search new2.gif (111 bytes)

 

log 2.JPG (76785 bytes)

Sharplex.jpg (28953 bytes)

MAHLEInd.jpg (21078 bytes)

 


Effluent Treatment
June 19, 2002

Introduction
Precipitation of Impurities
Solids/Liquid Separation
pH Adjustment

Neutralization
Oxidation
Associated Links

Arsenic
Copper
Molybdenum
Lime


Introduction

All acid plants produce some form of liquid effluent either from the process such as weak acid from a gas cleaning system, wash down water, accidental spills, boiler blow down, cooling water blow down, precipitation collected in a containment area, etc.  Some effluents are not treated prior to release to the environment while others must be treat extensively to remove contaminants before it can be safely discharged.

The purpose of an effluent treatment system is to treat the sulphuric acid plant effluents to generate a solids stream containing the impurities in the effluent and a liquid stream that is suitable for discharge to the environment or reuse elsewhere in the process.  The level and nature of the impurities in the weak acid varies considerably from plant to plant and as a result so does the treatment methods employed. 

In general, all effluent treatment methods employ the following steps:

Precipitation of Impurities

Impurities are generally metals which can be removed from solution by precipitation.  Precipitation can take place in low pH solutions (i.e. arsenic) or in high pH solutions (zinc, lead, copper, etc.).  The choice of precipitation methods is based on the solubility of the salt in solution, the subsequent disposal method and/or further processing of the salt.  Impurities are generally precipitated as hydroxides, sulphides, carbonates or chlorides with hydroxides being by far the most common.

Solids/Liquid Separation

Once the impurities are precipitated from the solution they are separated from the solution so they can be disposed of or sent for further processing and treatment.   The method used for solids/liquid separation will depend on the nature of the solids.  Initial de-watering of the stream can be done in a clarifier followed by filtration.  In some cases the stream is suitable for direct filtration to remove the solids.  Filtration may require the use of a filter aid to achieve the desired removal efficiency.

pH Adjustment

During the processing of the waste stream the pH of the solution may be adjusted many times.  The final pH of the solution may not be in the range required for disposal of reuse.  As such one final adjustment of the pH may be required.

Neutralization

Neutralization is the simplest way to treat a weak acid effluent.  As the pH of the solution increases, the solubility of various impurities changes causing them to precipitate from solution.

Sulphuric acid can be neutralized by the addition of calcium hydroxide (lime) to form calcium sulphate or gypsum according to the following reaction:

 H2SO4 + Ca(OH) 2 => CaSO4·2H2O

Calcium hydroxide is generally the least expensive and simplest to use neutralizing agent available for treatment of an acidic effluent.

Metal impurities will react to for metal hydroxides.

Impurity Form in Acidic Solution Metal Hydroxide
Arsenic H3AsO4 Ca3(AsO4)2
     
     

Oxidation

Where heavy metals remain in the stream after hydroxide precipitation, the addition of a chemical oxidant may be helpful to further enhance the removal of the metals.  In general, those metals with many oxidation states (i.e. iron, manganese, etc.) will precipitate more readily if they are in their highest oxidation state.  The use of hydrogen peroxide is effective in oxidizing metals to their higher oxidation state.