Stabilization/Solidification Characteristics And Mechanism Of Organic Clay Contaminated By Lead When Using Cement

The treatment of dredged silt has become a problem for society development.In the case of dredged silt with complex components like organic matter and potential toxic elements like Pb,Cu,etc.more factors need to be taken into consideration.The stabilization technique has been widely used in Civil Engineering or Environmental Engineering,however,there are limits of mechanism studies in these two domains.In particular,the existence of organic matter would not only weaken the strengthening and stabilizing effects of stabilizer like cement,but also have complicated effect on PTE stability.A laboratory study including unconfined compressive strength test,scanned electron microscope(SEM)and leaching test was conducted,to investigate how factors including cement concentration,lead concentration,humic acid(HA)and fulvic acid(FA)content,and curing age affect both geotechnical and environmental characteristics.Based on that,to study effects of different organic matter components on lead leaching concentrations,four soil groups with pure humic acid,pure fulvic acid,mixed acid,and none acid were set separately.Lead leaching concentrations were tested,after different incubation times,with/without 7 days' cement stabilization.The major conclusions are listed below:(1)When more cement is added or curing time increases,strength increases and lead leaching decreases,more hydration product appears,soil becomes denser and more solid.HA and FA would delay and inhibit stabilization reactions,thus with more HA and FA added,strength decreases significantly,and soil becomes looser.(2)Strength increases with higher lead concentration,and reaches a peak at a specific lead content in soil,then decrease with higher lead concentration.The lead content at strength peak varies,which may be due to soil type and water content.(3)The effect of humic acid on post-stabilization lead leaching concentration is dependant on incubation time.HA can facilitate the stability of lead in soil but weaken cementation reactions.With longer incubation time,the dominant mechanism gradually turns into facilitating lead stability by HA itself from weakening lead stabilizing effect of cementation.(4)FA can increase lead leaching concentrations of cement stabilized soil,and this effect lasts.FA can promote the activity of lead in soil,complex with lead and stay in aqueous phase,as well as inhibit the change from exchangeable lead to more stable forms.Meanwhile,FA weaken cementation reactions and lead stabilizing effect of cement.(6)In most cases,HA and FA co-exist with a ratio in soil,and the influence of soil organic matter on PTE stability is a co-effect of different components of organic matter.