Zeta potential and particle size measurement of humic acid-heavy metal complex

The word humus in gardening is often heard. The main component of humus is an organic component formed by corroding the leaves and stems of plants and is called a corrosive substance (humic acid substance). Humic acid is widely distributed in soil and natural water on the earth, and it has been said that it has a great influence on the supply of nutrients to plants. Due to its agricultural importance, research on fractionation and separation has been performed since the 1760s. In recent years, researchers have been interested in fields other than soil science, such as geochemistry, biology, environmental chemistry, and medicine, and research on their substances, roles, and applications has become active. At present, the following have been clarified regarding the properties of humic acid substances and their various effects on the environment.

[Effects on living things]

1. It promotes plant growth and has a microbial growth effect
2. When it photochemically reacts with insoluble manganese or iron oxides, these metals are reduced and ionized to dissolve, which increases their intake efficiency. 
3. There are some cases where it interacts with synthetic organic substances such as pesticides by various mechanisms to reduce the toxicity of compounds. On the other hand, pesticides that are difficult to dissolve in water may be adsorbed and dispersed. 
4. It has physiological activities such as anticoagulant and antiviral.

[Effects on the environment]

1. The humic substance has a surfactant activity and promotes the dispersion of oil that have flowed out to the ocean.
2. It is considered that the humic substance in water is involved in the production of organic chlorides such as trihalomethane in the water treatment process.
3. The humic substance forms a complex with metal ions.

Among the such effects of humic substance, we focused on the complex formation effect with metal ions. The particle size and zeta potential of the complex formed between humic acid and various metal ions were measured. Interesting results about the difference of the adsorption performance and stability of the complex are introduced.