TY - BOOK

T1 - Process development for the recycling of oil and gas drilling tools

AU - Kerschbaumer, Claudia

N1 - embargoed until 24-08-2023

PY - 2018

Y1 - 2018

N2 - Drilling tools for the exploration of oil and gas need to withstand mechanical stress, corrosion, and thermal gradients. Polycrystalline diamond compact drill bits (PDC bits) are designed to operate at such adverse conditions for much longer than the conventional drill bits made of steel. At the end of life the cutters made of polycrystalline diamond compact get removed to be recycled specifically. However, for the monolithic head itself there exists no economically viable way of recovery. The main body part consists of monocrystalline tungsten carbide and cast tungsten carbide grains infiltrated by a binder alloy of copper, manganese, nickel, and zinc. On the shoulder of the bit infiltrated tungsten forms the machinable connection to the drill string connector made of steel. The objectives of this work comprised the illustration of possible ways to regain tungsten containing components from the monolithic drill bit. The multitude of joined materials as well as the small contact area relative to the big volume present major challenges. Based on the review of literature on the hard metal recycling and the composition and production of PDC drill bits the semi-direct recycling constituted the most promising technique. Hereby, the binder alloy gets digested by a solution that at the same time does not result in the significant leaching of the tungsten containing compounds. By way of screening tests it was found that oxidizing agents were required for effective disintegration and that the big refractory particles got loosened once the binder alloy was dissolved. Kinetics tests showed that, in contrast to infiltrated WC, infiltrated tungsten formed a diffusion barrier that lead to a characteristic slowdown of the reaction. While acidic hydrogen peroxide rendered fast binder digestion it also resulted in high amounts of dissolved tungsten. Nitric acid on the other hand exhibited positive selectivity. However, this changes in the presence of iron when the accompanying metal ion propagates the digestion of tungsten which was uncovered in systematic powder tests. This thesis proposes a recovery method for tungsten containing components from PDC drill bits based on the selective leaching of the binder. It facilitates the reclamation of otherwise untreatable waste in a simple and energy-efficient fashion without any prior pre-treatment of the monolithic body.

AB - Drilling tools for the exploration of oil and gas need to withstand mechanical stress, corrosion, and thermal gradients. Polycrystalline diamond compact drill bits (PDC bits) are designed to operate at such adverse conditions for much longer than the conventional drill bits made of steel. At the end of life the cutters made of polycrystalline diamond compact get removed to be recycled specifically. However, for the monolithic head itself there exists no economically viable way of recovery. The main body part consists of monocrystalline tungsten carbide and cast tungsten carbide grains infiltrated by a binder alloy of copper, manganese, nickel, and zinc. On the shoulder of the bit infiltrated tungsten forms the machinable connection to the drill string connector made of steel. The objectives of this work comprised the illustration of possible ways to regain tungsten containing components from the monolithic drill bit. The multitude of joined materials as well as the small contact area relative to the big volume present major challenges. Based on the review of literature on the hard metal recycling and the composition and production of PDC drill bits the semi-direct recycling constituted the most promising technique. Hereby, the binder alloy gets digested by a solution that at the same time does not result in the significant leaching of the tungsten containing compounds. By way of screening tests it was found that oxidizing agents were required for effective disintegration and that the big refractory particles got loosened once the binder alloy was dissolved. Kinetics tests showed that, in contrast to infiltrated WC, infiltrated tungsten formed a diffusion barrier that lead to a characteristic slowdown of the reaction. While acidic hydrogen peroxide rendered fast binder digestion it also resulted in high amounts of dissolved tungsten. Nitric acid on the other hand exhibited positive selectivity. However, this changes in the presence of iron when the accompanying metal ion propagates the digestion of tungsten which was uncovered in systematic powder tests. This thesis proposes a recovery method for tungsten containing components from PDC drill bits based on the selective leaching of the binder. It facilitates the reclamation of otherwise untreatable waste in a simple and energy-efficient fashion without any prior pre-treatment of the monolithic body.

KW - Recycling

KW - hard metals

KW - tungsten

KW - tungsten carbide

KW - cast tungsten carbide

KW - hydrometallurgy

KW - semi-direct recycling

KW - refractory metals

KW - drill bits

KW - kinetics

KW - tungsten dissolution

KW - Recycling

KW - Semidirektes Recycling

KW - Wolfram

KW - Wolframkarbid

KW - Wolframschmelzkarbid

KW - Refraktärmetalle

KW - Hydrometallurgie

KW - Bohrköpfe

KW - Kinetik

KW - Wolframauflösung

M3 - Doctoral Thesis

ER -