Composite phosphorylated-modified rice straw prepared for highly effective immobilisation of cadmium in agriculture contaminated soil

Abstract

Environmental context Rice straw is generated in vast quantities each year, but although the cellulose structure is stable, only 20% is used effectively. The structure of rice straw gives it high porosity and active functional groups, which means it easily adsorbs metals, but few studies have applied it to metal-contaminated soil. This study showed that composite phosphorylated-rice straw can be highly effective for the immobilization of cadmium in contaminated soils. Rationale Rice straw is generated in vast quantities each year, but the effective utilisation rate is low. In order to develop full utilisation of rice straw and seek high-efficiency immobilising agents for cadmium contaminated soil, the objectives of this paper was to prepare a new modified rice straw material. Methodology Composite phosphorylated rice straw (CPRS) and phosphorylated rice straw (PRS) were synthesised, the apparent morphology and functional groups of CPRS and PRS were characterised by SEM-EDS and FT-IR, and the remediation ability of CPRS and PRS on cadmium contaminated soil were studied by pot experiment. Results The results showed that the order of maximum adsorption capacity (Qmax) for Cd2+ was CPRS > PRS > RS, Qmax of CPRS for Cd2+ was 53.57 g kg−1. CPRS had a richer porosity, evidenced a PO43−EN22041_IE1.gif group stretching vibration and had calcium salt well-dispersed on its surface. The application of CPRS to Cd contaminated soil significantly improved the plant biomass (fresh biomass increased 66.97%, over control) and decreased the Chinese cabbage uptake of Cd (decreased 67.16%, over control). The chemical stability of cadmium in soil was enhanced by applying CPRS due to a decrease in the exchangeable Cd in soil in proportion (decreased 95.38–99.10%) to the increasing fractions of Cd bound to Fe/Mn oxides (increased 141.15–158.90%), and residual Cd (increased 4.76–6.99 times) following the application of CPRS as compared to control treatments. Discussion CPRS had an excellent immobilisation ability for cadmium contaminated soil, which was related to improved soil pH and cation exchange capacity. It possibly immobilises Cd in the soil via surface complexation through Cd–O groups at the surface of CPRS. Modified rice straw materials could be highly recommended as an efficient stabiliser to immobilise Cd in polluted agricultural soils.