Synthesis and use of synthetic humic-like acid (SHLA) for the remediation of metal-contaminated water and soil

Humic acid (HA) can effectively bind several hazardous metals. The interaction between HA and metal ions plays an important role in metal mobility and bioavailability in the environment. Abiotic humification processes can provide a potential and promising way to synthesize humic acids with better metal binding ability than their naturally occurring counterparts. The aim of the PhD project is to investigate the synthesis and application of synthetic humic-like acid (SHLA) for water/wastewater treatment and soil remediation. This thesis showed the log K and complexation efficiency of SHLA were higher at higher pH, lower ionic strength, higher temperature and higher SHLA concentration, and the effects of the above environmental factors on the complexation reaction are similar to natural HAs. Eleven SHLAs were prepared via a range of abiotic humification conditions. The results showed that SHLAs with a higher content of carboxylic groups, more aromatic structures and a higher degree of humification, would have a better Cu complexation ability. The optimal abiotic humification conditions to synthesize SHLA with better copper complexation ability were also determined. When applied as a soil washing agent, SHLA was more effective than some common washing agents, like Na2EDTA, citric acid, commercial HA and tartaric acid, and reduced the bioavailability and environmental/human health risk of metals. When applied as an adsorbent, the adsorption process between SHLA and Cu2+ was favourable, spontaneous and endothermic, and was described by the pseudo-second-order kinetic model, Langmuir and Freundlich models. The Cu2+ adsorption capacity of SHLA was much higher than many of the humic acid-based materials reported in the literature and the SHLA can be regenerated by HCl. Besides, SHLA was able to remove co-contaminant metals from solution. When applied as a soil amendment, SHLA lowered the bioavailability of Cu, Zn and Ni, but increased the bioavailability of As. Besides, the addition of SHLA could increase TOC and WSC of soil but decrease the soil pH. This thesis has shown that it is possible to synthesize SHLAs that show great promise for use in remediation of contaminated water sources and soils.