Temperature Effects on Properties of Rice Husk Biochar and Calcinated Burkina Phosphate Rock

Vincent K Avornyo,Michael L Thompson,David A Laird,Andrew Manu

doi:10.3390/agriculture11050432

Vincent K Avornyo, Michael L Thompson + Show 2 more

Open Access

https://doi.org/10.3390/agriculture11050432

Copy DOI

Abstract

Rice husk biochar (RHB) and phosphate rock (PR) are locally accessible resources that poor farmers in Sub-Saharan Africa (SSA) can utilize to increase rice productivity. However, biochars are variable depending on feedstock, pyrolysis temperature, and duration. Phosphate rocks from SSA are of low solubility. The goal of this study was to determine whether pyrolysis of rice husk (RH), calcination of PR, and the calcination/pyrolysis of a RHB-PR mixture at 300 °C, 500 °C, and 700 °C can increase formic acid (FA)- extractable phosphorous (P). The properties of these RHBs were compared to the properties of RHB produced through a simple farmer-friendly pyrolysis technique termed “Kun-tan”. Properties of calcinated PR were also compared to the raw PR. Quartz formed from amorphous SiO2 during RH pyrolysis and was the dominant mineral phase in the biochars, irrespective of the pyrolysis temperature. Formic acid-extractable P content, pH, and ash content of the biochars increased with increasing pyrolysis temperature. At 700 °C, FA-extractable P content of the RHB was 219% more than the feedstock. Hydroxyapatite and quartz were the dominant minerals in the PR irrespective of calcination temperature, indicating that hydroxyapatite and quartz were stable to at least 700 °C. Rather, calcination decreased the FA-extractable P content of the PR.

Highlights

Large areas of the semi-arid regions of West Africa are covered by soils underlain by ferruginous crusts which are sesquioxide rich, humus poor, and kaolinitic
The X-ray pattern of the rice husk (RH) feedstock did not reveal the presence of quartz; the XRD patterns of the biochars were dominated by quartz peaks
The results suggest that quartz crystallinity increased with increasing pyrolysis temperature, because the 4.26 Å and 2.13 Å peaks of the 700 ◦ C produced Rice husk biochar (RHB) that was more intense than the peaks for biochars produced at lower temperatures (Figure 2)

Summary

Introduction

Large areas of the semi-arid regions of West Africa are covered by soils underlain by ferruginous crusts which are sesquioxide rich, humus poor, and kaolinitic. They are regarded amongst the least fertile soils in the tropics [1]. According to Amatekpor [2], the soils of northern Ghana developed over two main geological formations: the Birimian (Middle Pre-Cambrian) and the Voltaian (Lower Paleozoic). The soils developed from the weathered products of the Voltaian rocks are humus poor, rich in iron and aluminium oxy-hydroxides, and have a mineralogy dominated by quartz and low-activity clays with low effective cation exchange capacity [1,3,4,5]. The soils of large areas of northern Ghana are severely deficient in phosphorous (P), which is often the limiting factor for rice production in inland valleys [6]

Objectives

Methods

Results

Conclusion