IntorductionHumicsubstances play an vital role in nature. They can bind to heavy metal ions, whichare characterized by high toxicity and the ability to accumulate in theenvironment The typical dark colorationof these substances increases heat retention by soils helping in seedgermination.
They also elevate the buffering and cation exchan One of the mostcharacteristic properties of humic substances is their adsorption ability andin this way, they can influence the effectiveness of regeneration andpurification processes in soil and aqueous systems. Hence, the immobilizationor removal of toxic metals is a research goal as well as an industrial task ge capacities of soils Humicsubstances are popular for their high adsorption efficiency 1–4. Humic substances also interact with oxides,hydroxides, minerals and organic compounds to form compounds, which are solubleor insoluble in water, with different chemical and biological stabilities(Schnitzer, 1986). The formation of metal complexes and chelates with lowsolubilities, from the reaction between soil organic matter and metals, reducesthe probability of a toxic metal contaminate the groundwater (Tan, 1992). They can make bond with heavy metal ions,which have the high toxic rates and they have the ability to collect and mix inthe atmosphere. Process starts regeneration in the soil and they can affect theaqueous ecosystems 5–7. Therefore, the inactivation or excretion of these poisonoussubstances is the key work of research as well as an economic task. Aprofitable and environmentally-friendly method is the use of technology ofsorption founded on the use of sorbents composed from some bio-material 8,9.
Whenhumic acids, as the most efficient ingredients are used as an adsorbent formetal ions, their effect and sorption capacity greatly increased 2. When wecompare the humic acids of different availabilities like natural andcommercial, it shows that the industrial humic acids show a very high sorptioncapacity and a low degree of desorption 6, 12. While humic acids areseparated from oxyhumolite they showed a lower sorption capacity in comparisonwith humic soil-derivatives of humic acids 13. Connections betweenhumic acids and metal ions have a complex nature given by their heterogeneous,poly-electrolyte, and poly-dispersive character.
Metal ions can attach withhumic acids in different methods; due to the Wander Waal’s weak forces, highlynegative anions attraction etc result in the formation of other functionalgroups 1, 2, 4, 7, 14–16. Due to the heterogeneous character of humic acids andtheir partial solubility in water, there is a possibility of formation oforganic and inorganic mixtures of these metallic ions and other contaminants4, 17–21. Humic acids of low molecular weight had the highest sorptioncapacity than those of high molecular weight or un-fractionated humic material13. It was found that the binding of metals to humic acids depends on theircharacter. The sorption capacity of humic acids for some metals is much higherthan their possibilities given by the content of functional groups.
Metal ionsare attached to humic acids by different strengths and particular metals canexist in humic material in various fractions 4, 22–26.Due to the toxic effects of metal ions their removalfrom aqueous ecosystems is necessary. In this regard different methods wereapplied including precipitation, evaporation, electro-deposition, ion exchange,membrane separation, coagulation etc 24-26. But these methods are expensiveand having some disadvantages like secondary pollution. Therefore, we areapplying commercially available humic acid as an adsorbent to remove metal ionsfrom aqueous solutions.