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A chelator, potassium dipropyl dithiophosphate, and humic acid were combined and used as a stabilizing agent to study the stabilization effect of the mixture on heavy metals in a contaminated sediment. The results indicated that the stabilization efficiencies for Cu, Zn, Pb, and Cd in the sediment were up to 99.98, 90.66, 99.38, and 92.83%, respectively, and the unstable Cu, Zn, Pb, and Cd fractions fell by 57.11, 54.74, 56.41, and 89.14%, respectively, when 5% potassium dipropyl dithiophosphate and 7% humic acid were added. This significantly reduced the bioavailability of the heavy metals. Under leaching caused by simulated acid rain (pH 3 and pH 5), the heavy metals mainly migrated from the solid phase to the liquid phase during the initial leaching period, and the Pb, Cu, Zn, and Cd leaching rates in the sediment after stabilization fell by 55–99%. Cu showed the greatest reduction. When the results for the sediment after stabilization were compared with the sediment before stabilization, the wheat stem height had increased by 53.62%, the dry weights of the leaves and roots increased by 86.25 and 34.85%, respectively, and Cu, Zn, Pb, and Cd enrichment in the wheat roots and leaves fell by 40–88 and 73–95%, respectively.

In order to investigate the effect of total hardness on coagulation efficiencies of Al species, different Al coagulants – conventional Al salt (AlCl3), polyaluminum chloride (PAC-1) and the purified polyaluminum chloride (PAC-2) – were used to treat humic acid (HA) and kaoline clay in this study. The coagulation efficiency and coagulation kinetics were investigated by treating synthetic water with different total hardness. The results suggest that total hardness can influence the coagulation efficiencies of aluminum salts. The coagulation efficiency of AlCl3, PAC-1 and PAC-2 increased when total hardness increased. The investigations on coagulation kinetics showed that total hardness influences the flocs aggregation in the coagulation process of aluminum salts. Higher total hardness results in longer reaction time in all cases. The maximum floc size of AlCl3, PAC-1 and PAC-2 occurs when total hardness reaches 8, 4, and 1 mmol L−1, respectively.

Flocs generated in various aluminum coagulants treatment exhibit difference in size, strength and structure. The formation, breakage and re-formation of flocs were investigated by using a laser diffraction instrument (Malvern Mastersizer 2000, Malvern, UK). Different Al coagulants--conventional Al salt (AlCl(3)), polyaluminum chloride (PAC-1) and the purified polyaluminum chloride (PAC-2)--were investigated for the coagulation of humic acid (HA). The results showed the properties of HA flocs depend on which species of aluminum used. The monomeric and dimeric aluminum species (denoted as Al(mono)) formed the largest and strongest HA flocs with longest growth time. The HA flocs formed by Al(13)O(4)(OH)(24)(7+) (Al(13) for short) is the smallest and weakest. The properties of HA flocs made it possible to investigate the relationship between the flocs growth process and aluminum species.