Approaching Chemistry: Ferric Chloride for Wastewater Treatment

Industrial production generates a large amount of sewage and wastewater every day. To protect the environment and achieve sustainable development, we must adopt scientific methods for treatment. Why and how to use ferric chloride for wastewater treatment? Come and study with me.

What is ferric chloride?

The chemical formula of ferric chloride is FeCl₃, which is a black-brown crystal with thin flakes. It is easily soluble in water and has strong water absorption. It can absorb moisture from the air and deliquescence. It is non combustible. It has many industrial, pharmaceutical, and laboratory uses. Compared to its boiling point of around 315 degrees Celsius, its melting point is relatively low. When ferric chloride dissolves in water, it undergoes a hydrolysis process and releases heat in other exothermic reactions. Its solution is colorless to light brown and has a faint hydrochloric acid taste. It is corrosive to most metals and tissues. It is widely used for water purification and sewage treatment. In an anhydrous state, it is deliquescent. In addition, it absorbs water from the air and releases hydrogen chloride, which forms a thin mist in humid air.

Generally, the chlorination method is used to produce: using scrap iron and chlorine gas as raw materials, the reaction is carried out in a vertical reactor, and the generated ferric chloride vapor and tail gas are discharged from the top of the furnace and condensed into solid crystals in the collector, which is the finished product.

Ferric chloride for wastewater treatment

The largest application area of ferric chloride is in the water treatment sector, where its dilute solution serves as a flocculant and precipitant in water treatment, used for the treatment of domestic water, industrial water, municipal sewage, and industrial wastewater. When used for sewage treatment, it has advantages such as good effects and low price, but it also brings the disadvantage of yellowing watercolor. For example, the soap industry uses it as a coagulant for the recovery of glycerol from soap waste. Iron chloride is widely used in breweries due to its stable properties, easy preservation, high effective content, good phosphorus removal effect, and convenient addition.

The principle of using ferric chloride for phosphorus removal in brewery wastewater: The aeration tank is a reaction site for microbial treatment of wastewater, and ferric chloride is added to its outlet. On the one hand, it directly reacts with phosphate with its iron ions, and phosphorus removal is carried out through a part of the iron hydroxide colloid for net capture, adsorption, and flocculation precipitation; on the other hand, ferric chloride can improve the structure of microbial flocs, enhance their flocculation ability, and thus increase their ability to capture pollutants.

The water purification effect of ferric chloride is less affected by water temperature and pH, and it is inexpensive. It has a good treatment effect on some raw water (such as hard water). Its treatment effect on domestic sewage and industrial wastewater is also very good because it can not only precipitate heavy metals and sulfur compounds in sewage or wastewater but also form substances that can adsorb and remove impurities such as oil and polymers that are difficult to degrade in water. The phosphorus content in the treated water is also significantly reduced.

Overall, ferric chloride is used to treat industrial wastewater and can achieve the effects of sulfur removal, decolorization, oil removal, and COD removal. Compared to another substance commonly used for treating industrial wastewater - aluminum salts. Aluminum is still harmful to the human body. After aluminum enters the human body, it accumulates and participates in biochemical reactions, leading to toxic diseases such as senile dementia and aluminum-induced bone disease. In contrast, ferric chloride will not be toxic to living organisms. It is cheap, and the formed alum flower is easy to settle. It still has a good coagulation effect at low temperatures and low turbidity. The suitable pH range is also wide, and the removal effect of organic matter in water is better than that of aluminum salt.

Conclusion

In conclusion, we explore the subject of “ferric chloride for wastewater treatment”. Ferric chloride has strong corrosiveness, and the feeding equipment needs to undergo anti-corrosion treatment. Operators should be equipped with labor protection facilities. It should be stored in a cool, dry, and ventilated warehouse, protected from rain, collision, and contamination by toxic substances. It is not suitable for outdoor stacking.