Destabilization and aggregation of aqueous humic acids solution by metal ions

The aggregation of soil humic acid (HA) after addition of cations was investigated by nephelometric measurements of HA solution turbidity. Here we show that aggregation is promoted by the presence of positive ions in the solution and that the order of increasing effectiveness in turbidity follows Schulze-Hardy rule. Also, the obtained results indicate that the cation with the largest ionic radius within a common valence is the most effective coagulant. Influence of unions follows the sequence: chloride < nitrate < sulphate, but it is insignificant comparing the influence of cation. This confirms that HA molecules are of negative charge.